# Cycle Testing Observations…



## SilverFox (Apr 17, 2006)

Cycle Testing Observations… 

I have had several discussions about how batteries age during their use. Winny was so kind as to translate an article on battery cycle testing for me (many thanks Andreas), and I decided to see if I could answer some questions that I have had.

Cycle testing takes a large commitment of time and equipment. There is not a fast way to do this, and commercial equipment is designed around “standard” parameters that do not necessarily reflect the way we use our batteries.

I have been told that fast charging reduces cycle life, however I have been unable to get any specific numbers. This became the objective of this test.

I took two Sanyo 2500 mAh cells, performed a forming charge of 200 mA for 16 hours, cycled them 5 times, and proceeded with the testing.

Two chargers were compared. The Energizer 15 minute charger was the fast charger, and the Sanyo NC-MQH01U was used as the slow charger by utilizing one of the slow charge slots. The Sanyo charger charges at roughly a 1.0 amp rate in that slot.

The first test was done after charging both cells on the slow slots of the Sanyo charger. This became my base line capacity. The cells came out reasonably close in capacity and the testing continued.

I saved the data collected every 25 cycles, and it is presented below.

The procedure involved charging the cell on its respective charger, letting it rest for 20 minutes, then discharging it at 2.5 amps down to 0.8 volts. 

High capacity cells are not the best choice for high charge or high discharge rates. A cell is usually considered fully discharged at 0.9 volts, and going to 0.8 volts is a bit of an over discharge. These values were chosen to accelerate the aging process and reduce the number of cycles needed to see a trend. I also only let the cells rest when I was asleep. I believe you can get improved life by less rigorous usage.

A general consensus from a variety of battery manufacturers suggest that you can expect around 500 cycles from high capacity batteries, and around 1000 cycles from lower capacity batteries. Lower capacity batteries are those with less than 2200 mAh of capacity, however Energizer was the only one that suggest a 2200 mAh cell as lower capacity. Most consider 2000 mAh cells as the high end of the lower capacity cells.

Keep in mind that when the battery manufacturer comes up with these numbers, they are doing a 5 hour discharge and a 14-16 hour slow timed 0.1C charge. 

Also, keep in mind that all of the information I have been able to find indicates the number of cycles to reach around 60-80% of the cells original capacity. It is understood that the mid point voltage will be reduced, but the performance is measured in reduction of capacity.

In non regulated flashlights, the voltage retention under load is very important to the brightness of the light. It has been interesting to watch the voltage drop during cycling.

Here is the data from the slow charge through 150 cycles.







Here is the data from the fast charge through 150 cycles.






Here is a comparison of the slow charged cell at 125 cycles with the fast charged cell at 100 cycles. Based on this limited testing, it looks like you lose around 25 cycles by fast charging.






In my notes I observed that the fast charge cell was about done after 125 cycles. I then switched to “topping off” the fast charge at a slower rate on the Schulze charger. This did not seem to have much effect.

At 148 cycles, the fast charge cell was no longer able to be charged on the Energizer 15 minute charger. I would put the cell in, and would get a blinking red error light. The final charge cycles were done on the Schulze.

Out of curiosity, I did another cycle (number 151) on both cells. This time I charged both cells on the Sanyo charger and did the discharge at 1.0 Amps.






Conclusions:

Fast charging high capacity cells, followed by fast discharging to an over discharged state is harder on the cells than slow charging followed by the same conditions.

The mid point voltage drops with use and it seems to drop faster with fast charging.

Cycle performance based on a percentage of remaining capacity does not tell the whole story.

Cells stressed and damaged by heavy usage may still be suitable for lower drain applications.

The performance lost by cycling is permanent.

There does not appear to be an increase in the self-discharge rate of high cycled cells.



Here is round 2 of this effort. I was wondering how smaller capacity cells would handle this. I took some Titanium 2000 mAh cells and decided to test them under the same conditions. The same chargers were used, and the discharge remained at 1C, which, in this case is 2.0 amps. 

I did change one thing. After 50 cycles, I decided to do a 0.1C charge for 16 hours after every 25 cycles. These cells seemed to be able to handle the cycles a lot better than the higher capacity cells did. I am not sure if the forming charge made any difference or not. 

There was no problem charging on the Energizer 15 minute charger, and while the cells have lost some capacity, they still seem to be in reasonable condition. 

Here is the data from the slow charge through 150 cycles.






Here is the data from the fast charge through 150 cycles.






Here is a comparison of the slow charged cell at 125 cycles with the fast charged cell at 100 cycles. Based on this limited testing, it looks like you lose around 25 cycles by fast charging. This is the same result that we saw with the Sanyo 2500 mAh cells.






Once again, I did another cycle (number 151) on both cells. This time I charged both cells on the Sanyo charger and did the discharge at 1.0 Amps.






Conclusions:

Lower capacity cells handle cycle testing better than higher capacity cells.

Lower capacity cells handle fast charging better than higher capacity cells.

It seems that fast charging performance drops off faster than slow charging performance, buy around 25 cycles.

Based on this limited amount of testing, I can believe that these cells may be able to go 300-500 cycles. Looking at the data from the 1.0 amp discharge at cycle 151, the slow charged cell is at 95% of the original Amp Hours and 91% of the original Watt Hours. The Fast charge cell is at 94% of the original Amp Hours and 88% of the original Watt Hours. Cycle testing usually goes to 80% of the original Amp Hour capacity, so these cells still have a ways to go. 

It would appear that the price you pay for higher capacity is a loss of power and cycle life. Of course, this test is designed to accelerate the process. Charging and discharging at lower rates may give you some additional cycle life.

Round 3

This time the testing involved Sanyo Eneloop cells. These cells have a low self discharge rate and are supposed to maintain about 85% of their initial capacity after a year of room temperature storage. These cells may be sensitive to extended trickle charging as well as high charge rates. 

These 2000 mAh cells were charged on the Energizer 15 minute charger which uses a 7.5 amp charge rate. That works out to charging at around 3.75C. Discharging was done at 1 amp this time, and every 25 charge/discharge cycles a 16 hour charge at 200 mA was done.

It was interesting to observe the performance of these cells. They started out having an internal resistance of 0.026 ohms. They held, or slightly increased in capacity over the first 100 cycles, then they started to fade. Looking at the graph you can see this fade in cycles 125 and 150.

I then charged them back up and let them sit for 30 days. It appears that this ultra rapid charging has effected the cells ability concerning low self discharge. Also, the cells internal resistance rose to 0.340 ohms. Discharge 151 on the graph has a very interesting shape to it. The Energizer 15 minute charger now rejects these cells. When I charged them up and put them into my camera, I got a low battery warning after 15 shots. I was able to coax another 8 shots before the camera powered down. I usually get several hundred shots from a set of Eneloop cells.

It looks like these cells can handle 100 – 125 charge cycles on the Energizer 15 minute charger, but after that they are about done. The Titanium 2000 cells came in better than these cells did, but they are not low self discharge. Overall, I was impressed that they held up as well as they did, but for longer cycle life it would be better to keep the charge rate in the 0.5 – 1.0C range.

Here is the graph.







Tom


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## JimH (Apr 17, 2006)

Tom,

Fantastic report



. That sure looks like a whole lot of work. How many months did it take to run through all those cycles?


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## bcwang (Apr 17, 2006)

So much for the 500 cycle claim, unless they aren't designed for the 3 amp discharge rate. I guess I should stop refreshing my batteries every so often, I'm just killing the cycle life.

By the way, what is it with the last set of graphs looking like a hill. The voltage actually went up during testing?


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## TinderBox (UK) (Apr 17, 2006)

hello silverfox

excellent work as usual.

I think the sanyo 2500 did very well after 150 cycles in 15 min charger at 7.5 amps.

I am more suprised at the capacity loss on the slow charged battery`s of 228mah compared to the new cell.

unless you have a hard to find, or expensive battery pack.

it looks like fast charging is the way to go.:rock:

regards.


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## JackJ (Apr 17, 2006)

bcwang said:


> So much for the 500 cycle claim, unless they aren't designed for the 3 amp discharge rate. I guess I should stop refreshing my batteries every so often, I'm just killing the cycle life.


 
I too wonder about frequent refreshing or "topping off", but I'm not sure this particular test helps out in knowing whether this is a good practice, since the use pattern is pretty extreme.

I recently acquired a new Lux V bike light that uses 4 AA NiMH's. The light has a low battery indicator that comes on at about 1 hr. 40 mins. However, at that point the cells still indicate 1.2 v (with no load). Silverfox--do you how much recovery is normal, i.e., what voltage cells discharged to 0.8 v read after a rest period of say an hour?

I want to thank you for all the work you've put into this, and other similar projects. Based on your initial reports, I bought the Energizer 15 min. charger, since there are times I just can't wait a couple of hours for cells to be topped up. I'm still very happy with the purchase, even though it's not as gentle as a slow charger. 

Jack


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## SilverFox (Apr 17, 2006)

Hello Bcwang,

Keep in mind that the results are for 100% depth of discharge cycles. I believe that if you re-charge frequently, the actual number of cycles goes up exponentially.

I saw the "hill" several times. It seems that under this load, the cell recovers slightly when the chemistry heated up. I found it very interesting...

Tom


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## SilverFox (Apr 17, 2006)

Hello Jack,

Until the last few cycles, both of these cells recovered to 1.18-1.20 volts after the discharge cycle.

Tom


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## HarryN (Apr 18, 2006)

Thanks Tom - Great work.


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## koala (Apr 18, 2006)

Hi Tom,

This post is important. Thank you for posting your findings.

vince.


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## wptski (Apr 18, 2006)

Tom:

Nice work Tom!  The only thing that I question is in "realtime" use .8V/.9V is below the level that a battery powered whatever may show a low battery. I've only check two things so far, a Fluke 189 DMM and a RS Pro 94 scanner. The scanner started beeping low battery at 1.15V per cell and the the DMM was 1.12V if my memory serves me correctly. Of course your tests are full cycles but I wonder how this same test would fair with a 1.1V cutoff?

EDIT: Corrected voltage typos.


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## chimo (Apr 18, 2006)

Wow Tom, outstanding work. It must have taken an enormous amount of time running these tests and compiling the data. Thanks for doing this. :rock: :goodjob: 

Paul


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## SilverFox (Apr 18, 2006)

Hello Bill,

I am not sure how much influence discharging to a lower voltage had on the cycle life of the cells. They would usually rebound to around 1.2 volts after the test.

I believe your applications are drawing less current and using more than one cell. If I were checking a pack, I would stick to a 1.0 volt cut off.

At any rate, I chose the lower cut off in an effort to accelerate the test. I really didn't want to spend all my time testing... There are flashlights to play with... oops I mean use.  

Testing is done to answer questions. However, in the course of conducting the tests, it seems like a whole new group of questions arise. This test was no exception.

Tom


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## wptski (Apr 18, 2006)

SilverFox said:


> Hello Bill,
> 
> I am not sure how much influence discharging to a lower voltage had on the cycle life of the cells. They would usually rebound to around 1.2 volts after the test.
> 
> ...


Tom:

Gosh! Bigtime typos above! That should be 1.15V and 1.12V per cell.

Yes, my applications do draw less current but does that matter? Often as seen in your Ni-MH shootout thread, discharge capacities hardly varied much between .5A and 1A. I wonder how much capacity varies between .9V and 1.1V? The discharge voltage on any charger is based on cell count wether it's auto/manually.


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## evan9162 (Apr 18, 2006)

I've done plenty of discharge tests manually with a current load and DMM, and have watched the voltage change over the discharge curve. 1.1V to 0.9V happens in only a few minutes during a 0.5C discharge test. In reality, the added runtime from discharging to 0.9V isn't worth the risk of reversing cells, especially in larger packs.


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## snakebite (Apr 19, 2006)

now to see what the reduction in capacity is caused by.
perform a flash amps test on a set of 3 cells.
1 new,the high rate,and the low rate.
or test with an esr meter if you have one.
post results.
a more controlled test would have done this at the start but a new unabused/cycled cell is a decent control if its from the same batch.


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## 2dim (Apr 19, 2006)

Thank you so much for kindly sharing your knowledge with us...always carefully tested and right up to date, too.

I can't help wondering whether Rayovac IC3 batteries, using their 15 minute charging system, would show similar results.

I've noticed there is now another proprietary 15 minute charger here in Canada, under the Noma brand name.

With Rayovac discontinuing theirs, do you know if the Noma batteries might be interchangeable?


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## Handlobraesing (Apr 20, 2006)

bcwang said:


> So much for the 500 cycle claim, unless they aren't designed for the 3 amp discharge rate. I guess I should stop refreshing my batteries every so often, I'm just killing the cycle life.
> 
> By the way, what is it with the last set of graphs looking like a hill. The voltage actually went up during testing?




Sanyo Twicell design sheet shows capacity is beyond initial capacity after 100 cycles and drops to 80% after around 430 cycles based on C rate charging(-10mV termination) 1h rest, C rate discharge, 1h rest... and repeat. 

Their end of discharge votlage was 1.0v. Silverfox used 0.8v.


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## bcwang (Apr 20, 2006)

Handlobraesing said:


> Sanyo Twicell design sheet shows capacity is beyond initial capacity after 100 cycles and drops to 80% after around 430 cycles based on C rate charging(-10mV termination) 1h rest, C rate discharge, 1h rest... and repeat.
> 
> Their end of discharge votlage was 1.0v. Silverfox used 0.8v.



Wow, if .8v vs 1.0v makes that much of a difference, I'd better charge my batteries early. Some of my devices can easily bring down the voltage below .8 before the device dies. I wonder if the .9v used by the lacrosse hurts cycles any worse than using 1v as the termnation point.


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## SilverFox (Apr 20, 2006)

Hello Handlobraesing,

I am not sure what data you are looking at, but I was only able to find information for the HR-4/5AU cells. These cells are rated at around 2100 mAh, and should perform differently than the 2500 mAh high capacity cells.

It seems that once you get over 2000-2200 mAh capacity, things change. 

Tom


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## Handlobraesing (Apr 21, 2006)

Tom,
http://www.sanyo.com/batteries/pdfs/twicellT_E.pdf is the paper I'm talking about.
In the charging method, it says:
"Set the charge current at a value between 0.5It and 1It.*** during quick charging"

As an exception, they define maximum charging current for HR-4/3AU and HR-4/3FAU as 3.0A. 

A few sentences below, it says "If charging is performed at a current exceeding the maximum allowed current (1It), the rate of oxygen gas consumption at the negative electrode will not keep up..."

Sanyo uses "It" to refer to the charge rate and it means the samething as "C" that is more commonly used.


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## js (Apr 26, 2006)

Tom,

Fantastic work as usual! Thank you so much for all of the info that you selflessly provide to us. It has been invaluable to me on more than one occasion (as you know  )

I assume that when you say "It seems that once you get over 2000-2200 mAh capacity, things change" that you are talking about AA cells only, right?

Because a 2000 mAh sub-C NiMH would definitely be a LOW-capacity cell, and a 2000 mAh AAA cell would be incredibly HIGH-capacity. My point is too obvious to belabor further. Unless I'm wrong, of course, and then please feel free to belabor it.

Anyway, Tom, really, THANK YOU for this. Incredible information and very enlightening and revealing. I never would have thunk it.


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## david (Jun 17, 2006)

look at this
*New Products *

*Vapex Offers New VTE2000AAP NiMH Battery*

January 15, 2004







*Vapex Technology Ltd.* (Hong Kong) unveiled its new VTE2000AAP rechargeable nickel-metal hydride (NiMH) battery, which has a high energy density that is 15% over the normal 1,800mAh battery, a high drain performance of up to 3C, and a high shelf life that is 80% of the initial capacity storage for two years.


WHAT do you say ? Anyone has it ?


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## bob_ninja (Jun 20, 2006)

*Re: Cycle Testing Observations…*

First thanks for the effort, we appreciate it.



SilverFox said:


> Two chargers were compared. The Energizer 15 minute charger was the fast charger, and the Sanyo NC-MQH01U was used as the slow charger by utilizing one of the slow charge slots. The Sanyo charger charges at roughly a 1.0 amp rate in that slot.....
> 
> Tom



I am bit puzzled by your terminology. I would call the 15 min charger "super-fast" and the Sanyo @ 1 / 2.5 = 0.4C a "medium speed". I thought that 0.1C (250mA) used for the forming stage is a "slow speed". Not to split hair, the reason I bring this up is that some people prefer longer cell life to 15 min convenience. For instance, I simply have a set of backup Alkiline cells for the times when I am in a rush and just don't bother with "super-fast" or even "fast" speeds.

When I got my BC900 I used the default 200mA rate - "slow". Due to the issues brought up here I switched to 500mA rate which is still "slowish" according to my terminology. My objective is to get a longer cell life.

In fact, many uses are a low to medium power draw, such as wireless mice, wall clock, MP3 players, etc. They are not as demanding as


SilverFox said:


> then discharging it at 2.5 amps down to 0.8 volts.



Now I realize this method was chosen for speed, so don't suggest you test other "slower" scenarios, fair enough. My question is if there is a way to extrapolate from your tests or some other trick to derive from your tests results for this other scenario?

"Slow" (0.1C to 0.2C) charge rate and "low" power draw rate (max 0.3C)

For me at least this scenario would represent the majority of uses, hence I am more interested in it. It is especially relevant to the multitude of electronic gadgetry that doesn't have electric motors or other moving parts.

Again, not to diminish your work, it just doesn't represent most of my use scenarios. The tests seem to show that after 150-200 cycles the cells were degraded, unusable for most applications, compared to claimed 500-1000 cycles. I thought NiCd handles about 1000 cycles and NiMH handles about 300-500 cycles (might have read it at the battery university site). I wonder if the "slow/low" scenario would get much closer to the 500 figure.

As an example from real-life slow/low scenario, I have solar lights in my driveway. Each has a pair of NiCd AAs and a LED light. Clearly it is a slow charge rate as solar panel is small. I assume it is a low power draw as LED is tiny compared to reular flashlight lamps. From the original set most of them have suffered from "accidents" (lawn mower and such). The 3 remaing lights still work very well. I think they are about 3 years old, which is 3 x 365 = 1000 cycles. In fact, they survived temperature range from -30C to +30C.

Hence cells can last a very long time and even exceed specs.

Again great work on your part and I am not attacking/criticizing it. Just wondering if there is a way to estimate slow/low scenario cycle life without spending yet more time/effort.

thanks


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## SilverFox (Jun 23, 2006)

*Re: Cycle Testing Observations…*

Hello Bob,

I believe most of the test data that suggests 300-500 cycles has been done with lower capacity cells. I need to do another round with 2000 mAh cells and see if they hold up better.

I believe the only way to get the information you are looking for is to test using 0.1C charging and 0.3C discharging. Unfortunately, several hundred cycles would take a lot of time...

I got about 5 years out of my NiCd cells in my solar yard lights. I don't think they were full cycling every time, but in the winter they never completely charged up. However, they were only 900 mAh cells. I replaced them with 1000 mAh cells and they are working fine.

Tom


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## VidPro (Jun 28, 2006)

Silver thanks for taking the effort to do this and represent the data.


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## SilverFox (Sep 23, 2006)

Update:

I am doing a test on Titanium 2000 mAh cells. I am using the same chargers and will follow the same test procedure, however since I am seeing a similar drop in voltage I will be adding a "forming" charge every 25 cycles. This should give the "best" chance for the most cycles.

Testing in progress...

Tom


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## jtr1962 (Sep 23, 2006)

I just looked at this thread for the first time. Very interesting results. I would be interested in seeing if there is any improvement in cycle life using reflex (also known as burp) charging, and also if this charging method can revive the cells which have lost their capacity. Problem is I'm not aware of any commercial chargers which use reflex charging. Also, while the number of cycles you're getting seems low you're stressing the cells much harder than most normal usage. Still, the results are encouraging. Even with fast charging you get 100+ cycles before significant capacity is lost. In a situation where someone recharges their cells once a week that's two years of use. From a cost standpoint (compared to disposable cells) that comes to $0.03 per cell (assuming the Sanyos cost $3 each). That's still an order of magnitude cheaper than disposables.


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## Anders (Sep 23, 2006)

Thankyou Silverfox for the hard work you are doing for CPF.

Your threads is the first i read every day and in most cases the most interesting ones.

Anders


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## MrAl (Sep 23, 2006)

Hi there,

Just a note for some that were talking about partial charging their cells
more often...

A partial charge does not count as a full cycle. You can probably top off
your cells many times before it equates to having used one full charge cycle.


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## SilverFox (Sep 23, 2006)

Hello JTR,

The ICE charger can do reflex charging, but it won't bring the cells back to life. I have tried several chargers (including the Schulze and ICE, and others) and several charge rates and have not been able to get the test cells to "recover."

Tom


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## jtr1962 (Sep 23, 2006)

SilverFox said:


> The ICE charger can do reflex charging, but it won't bring the cells back to life. I have tried several chargers (including the Schulze and ICE, and others) and several charge rates and have not been able to get the test cells to "recover."


Well, I had to ask.  I haven't had any luck trying to get bad cells to recover, either. I have a few cells from a batch of 50 1800 mAH Nexcells which have the same symptoms as your cycled test cells (lower discharge voltage, much less capacity). They didn't go through that many cycles, either.

To add to the mix of possible variables you might test for I wonder if fan cooling will extend the number of cycles significantly. Lately I always use a fan regardless of charge rate. It seems like it delays the charge termination a bit while preventing the cells from getting anything beyond slightly warm, even at 1000 mA. I'm wondering if heat is the primary failure mechanism for NiMH/Nicad. Might be something worth testing for.

I've thought of doing something like this myself on occasion when I have the time. I'd probably want to automate the process somehow. Too bad the BC-900 doesn't have the ability to go through some set number of cycles.

Anyway, great work. :thumbsup: This thread is yet another valuable resource which you have contributed to CPF. :twothumbs


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## Billson (Sep 24, 2006)

jtr1962 said:


> Even with fast charging you get 100+ cycles before significant capacity is lost.



jtr,

What rate is considered fast charging? I have a couple of Sanyo 2500's that have virtually died after less than 50 cycles. Their capacity have decreased to around 2100mah and self-discharges to below 1.2V in about 3 days. I have never charged it at more than 1A on the La Crosse charger so I'm quite curious. I have dropped the cells a few times though.


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## SilverFox (Sep 24, 2006)

Hello Bill,

Fast charging is usually charging in 1 hour, or less.

Tom


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## Billson (Sep 25, 2006)

Hi Tom,

Thanks for the clarification. I must have gotten some bum cells then.


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## SilverFox (Nov 5, 2006)

Update:

I am nearing 150 cycles on the Titanium 2000 mAh cells. They are handling this charging and discharging test a lot better than the Sanyo 2500 mAh cells did.

With 2000 mAh, or less, cells, I can believe you could get over 500 cycles with "less stringent" use. These test cells may still be "usable" after this test. I will have to charge them up and check the self discharge rate... mmm, just what I need, more testing...  

I only have a few more cycles to go, then I will post the results.

Tom


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## JimH (Nov 6, 2006)

Silverfox, Thanks for all the effort you are putting in on this project. The biggest problem with this kind of testing is the amount of time it takes. By the time you come up with useful results on a particular battery, that battery is obsolete (at least for those of us in constant quest for the latest and greatest).

I think the most useful results of your testing would be the ability to say that, on average, batteries produced by company "C" perform better than batteries produced by "company A" (subject to constant reevaluation).


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## paulr (Nov 6, 2006)

Failure mode I've encountered with Sanyo 2500 mAH is they don't lose capacity but they develop a rather fast self-discharge (a few weeks instead of several months). I've killed several NiMH cell phone packs without heating them much, by simply overcharging at 0.2C for a day or two (stupid Motorola so-called "Intellicharger" has no smart charge termination at all). Overall I think all these claims of 500-1000 cycles are just marketing fantasy, like 100,000 hour LED life, maybe under lab conditions but not in the real world. In a decade or so of using cell phones, laptop computers, etc. I've never gotten more than 100 or so cycles out of any kind of packs.


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## WildChild (Nov 6, 2006)

I think the Sanyo had problems with high self-discharge at the end of 2004, early 2005. Same thing with Energizer 2500 mAh made in Japan. All mine developped high self-discharge within 5-6 cycles. I have some Sanyo 2500 mAh manufactured at the end of 2005 and so far, no problem with high self-discharge after over 10-15 cycles.


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## NiOOH (Nov 6, 2006)

Thanks Tom for all the time, effort and money you have put into these tests!Interesting results indeed. Your results and observations are similar to mine, i.e the newer high capacity cells are not very durable. Here is my example. I have 4 AA 1600 mAh Kodak cells (Made by Sanyo), which I use since early 2003. They have estimated a minimum of 300 cycles, at least 100 of them deep. They have been charged on various chargers (Lenmar Mach1, Conrad CM, Lenmar Pro66, LP 4KN, BC-900 etc)These cerlls are testing 1450-1500 mAh at 0.5 A discharge current, maintaining above 1.2 V for 2/3 of the discharge time. For comparison they tested little above 1600 mAh when they were new. In short, I consider these cells reasonably healthy and still use them. In contrast, my 2500 mAh Sanyo Industrial cells are showing signs of age after only a year of use and about 100 cycles. One of them self-discharges faster than the others, not cathastrophically, but still faster. 2 other cells show 10% lower discharge capacity compared to when new. I am planning to match 4 cells and retire the the other 4 alltogether. These cells were charged at max current of 2 A, i.e. not even 1C and often less, using mostly relatively gentle chargers. 

And another question question to Tom. I see you are using NC-MQH01. Have you measured the trickle charge current of this charger? I bought one recently, to replace my broken Pro66. Do you have any other comments on that charger? To me it's quite good. Sanyo states that it uses PVD for termination and the cells (especially the outer slots) are not heating much. I only wish it had 4 separate charge indicators.

Thanks once again.


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## SilverFox (Nov 6, 2006)

Hello NiOOH,

One of the "features" of the Sanyo is that it does not trickle charge. The charge stops when the light goes out.

I have noticed that severally mismatched cells will not fully charge in one cycle. This does not happen each time, but I have noticed it on a number of occasions. 

I like the charger. I gave one to a friend of mine that killed his cells by leaving them to trickle charge for extended periods of time. It is nice to have the option of two charging currents and the battery checker seems to work reasonably well. It also seems that there is wider spacing between the charging slots to keep the cells cooler.

Tom


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## bob_ninja (Nov 6, 2006)

NiOOH,

I have been having a lot of problems with Energizer 2500s. In one high draw application they kept collapsing early, like to almost 0V. Now I removed them from that use. In a music box for my kid they seem to have developed a memory effect and had to cycle them on BC900 to bring them back.

I am using Sanyo 2500s for high draw and they are doing much better. Also, my older 2K and sub-2K cells are fairly reliable. I wonder if I should avoid 2K+ cells altogether. Seems manufacturers are sacrificing a lot of other attributes (such as cell lifespan) in order to achieve 2.5K+ capacity.

I even paid too much for Eneloops just so that I can have a reliable standby batteries I don't have to top off all the time.

I use Sanyo charger for the initial charging @1amp until they batteries warm up. Then I transfer them to BC900 @0.5amp to finish at lower rate, cooler.

Anyway 100+ cycles for 2.5amp batteries is a joke. I consider any battery that handles less than 300 cycles a failure.

Oh, and looking forward to an update; thanks Tom 

P.S.: I am almost tempted to test a 2K cell on BC900 at 0.5 charge, 0.25 discharge (very slow rate based on Tom's scale


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## BentHeadTX (Nov 6, 2006)

More good info from SilverFox as always
My battery eater is a MillerMods UWAJ 1.7 watt L1P bicycle helmet light. Those poor AA cells get hit with 1.7 amps of current draw and I have noted the 2500's just don't have a decent capacity for this. 
Figure I'll go with the Titanium 1800mAH cells for high current drain applications, if it will do 18 amps--it should not have a problem with 1.7 amps. Must keep the voltage from sagging to Miller's constant current regulator to keep the light bright.


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## NiOOH (Nov 6, 2006)

Hi Tom.

My observation on the MQH01E (the European model that is) show that it does have a trickle charge. Thi is how I tested it:
As soon as the light goes out, i.e the charger has finsihed, I removed one cell and measured its OCV. It measured 1.42V. I waited for 4 hours and then measured again. The same cell showed 1.38. The remaining 3 cells were left in the charger. I took them out and measured them. All showed 1.41-1.42 V. The only conclusion I could make was that there is a maintenance charge on my MQH01E. Also, the charger continued to make these thicking noises even after the light goes off. 
The easiest way to to test this would be to connect a multimeter to one of the slots. I've been thinking to do that, but couldn't find thin enough copper plates. If you have some improvised setup, handy, you may try it. Otherwize, I a'm planning ti go to the hardware store the comming weekend to do an extensive shopping and may put something together


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## bob_ninja (Nov 7, 2006)

NiOOH,
I thought I read some place that it does provide trickle charge after the charge light turns off.


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## NiOOH (Nov 7, 2006)

Hi Bob. 
So far my measurements show that it does indeed. I'll do some more testing soon.


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## bob_ninja (Nov 8, 2006)

NiOOH,
I can no longer find info on trickle charge (might have read it in an older post here). The only indication of tirckle charge presence is in the decription of the LED:
"OFF stand-by or charge complete"
From the Kodak K6000 (which appears to be the same charger)
"LED off = power off, not charging, charger finished"

Since it makes a distinction between "not charging" and "charger finished", I would assume finished mode is using tickle charge.


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## SilverFox (Nov 8, 2006)

Hello NiOOH,

I conducted the same test as you did and I do not think it does a trickle charge.

I took two matched cells, I charged one of them on the Sanyo charger and the other on the BC-900. At the end of the charge, the cell on the Sanyo charger was at 1.45 volts, and the cell on the BC-900 was at 1.46 volts. 12 hours later, the cell on the Sanyo charger is reading 1.40 volts, and the cell on the BC-900 (which is trickle charging at roughly 17 mA) is reading 1.51 volts.

I then removed the cells from the chargers. Measuring them after 4 hours I show 1.40 volts for the cell that was on the Sanyo charger, and 1.42 volts for the cell that was on the BC-900 charger.

My conclusion is that the Sanyo charger (at least the one that I have) does not trickle charge.

Tom


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## NiOOH (Nov 8, 2006)

Hi Tom. Thanks for the test. This weekend I'll conduct sme more testing with mine. I guess there is a difference between the chargers. Mine is MQH01E, i.e the European modification. I believe yours is the U-model that does a cell check on slot #1. Mine does not have this feature, but trickle charges instead. I'll make some flat plate electrodes and will connect a multimeter to it.

And some comment on your measurements. I assume you set the BC900 to charge at the same current as the Sanyo. Was it the slow slot on the BQH01 (ca 1 A) compared to 1 A charge on the BC900? I ask because my BC900 maintains higher trickle current after charging at 1 A. I think it was 50 mA. Also your voltage reading seems a bit high for a cell that is trickled at 17 mA. 1.51 V looks more like a peak voltage during quick charge. Did you get an agreement between your measured values (I suppose using a multimeter) and the value shown on the display of the BC900?


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## SilverFox (Nov 8, 2006)

Hello NiOOH,

Yes. My charger has the state of charge tester, but it is in slot 2.

I used the 1.0 amp charge slot on the Sanyo charger and charged the other cell at 200 mA on the BC-900. All voltage measurements were taken with my Fluke meter. The cell on the BC-900 had finished charging about 10 minutes prior to me taking the voltage measurement.

12 hours on trickle charging does have an impact on the cells. That is why I don't recommend leaving cells to continually trickle charge.

Tom


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## NiOOH (Nov 8, 2006)

Hi Tom.
Thanks for the info. Somehow I don't thing this test is conclusive. You were using two chargers at quite different charging currents. What I did was to use only the Sanyo with 2 matched cells. One was removed shortly after the light went off and its OCV measured within 10 sec. The other was left for sevral hours on the charger and then taken off and measured. The one remaining on the charger showed higher OCV, which led me to believe that there must have been some current flowing to it.


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## SilverFox (Nov 8, 2006)

Hello NiOOH,

On the contrary...

The purpose of the test was to check for the presence of a trickle charge. These cells end up with a voltage of around 1.5 volts under the presence of a trickle charge and drop down to around 1.4 volts with no trickle charge. The cell on the Sanyo came off the charger (after 12 hours) at around 1.4 volts. The cell on the BC-900 with a very low trickle charge came off at around 1.5 volts. 

Just for fun, I took the cell that came off the Sanyo charger and placed it in the BC-900. It registered as fully charged and is trickle charging at about 16 mA. The voltage has climbed to 1.49 volts. 

So, if the Sanyo charger had a trickle charge, the cell should have been close to 1.5 volts. Since it didn't, I can conclude that the Sanyo charger does not trickle charge.

Tom


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## SilverFox (Nov 8, 2006)

Update:

I have posted the data from the testing on the Titanium 2000 mAh cells in the first post. They handled the cycle testing better than the Sanyo 2500 mAh cells did.

Tom


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## SilverFox (Nov 11, 2006)

I have been thinking about this test. I often find that you set out to find the answer to a question, but during, and after, the testing, more questions come up.

There are two influences at work during these tests. Charge rate, and discharge rate. I don't believe the 1C discharge rate has a drastic effect, so that leaves the heat generated during the charge cycle.

I recently read an article suggesting that the anode and cathode materials are not thermally balanced. The have a different rate of thermal expansion. This allows some sliding back and forth, that can wear down the separator. When the separator wears thin enough, soft shorts start to form, and the battery capacity goes down and the self discharge rate increases.

In the quest for higher capacity cells, the manufacturers are thinning down the thickness of the separator. Add to this some heat from the rapid charging and we have greatly reduced cycle life.

I find it interesting that the battery manufacturers are giving us higher capacity cells, along with 15 minute chargers. Perhaps this is a way to increase the sales of batteries...

I decided to take a look around and see if I could find some 2000 mAh cells. They are hard to find. Then I remembered the Eneloop cells.

I find it interesting that Sanyo came to market with 2000 mAh cells. They are advertising 1000 cycles along with their very low self discharge rate. This suggests, to me at least, that engineers had a lot of influence over these cells. 

I also find it interesting that the other low self discharge cells are labeled with slightly more capacity, and a slightly higher self discharge rate than the Eneloop cells.

Could it be that 2000 mAh is the magic number?

I have been hearing about high rates of self discharge with high capacity cells. In the RC crowd, they are finding that the newer high capacity cells are fragile, and while they do deliver longer run times, they need additional care, or the cells die.

Perhaps our quest for higher capacity is a little misguided. We may want batteries that are more robust, at the expense of some capacity. In marketing, higher numbers seem to sell better, so I guess there would have to be a paradigm shift to get the manufacturers to go back to 2000 mAh cells.

Tom


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## NiOOH (Nov 11, 2006)

Hi Tom.

I share your toughts. When Sanyo 2500 mAh cells came on the market I was excited, and got a couple of industrial-grade sets at once. Now, a year and a half later, I can no longer rely on them for critical applications. They'll be going to long term strorage, probably never to return in service. I replaced them with with a set of 2100 mAh cells and another that is 1700 mAh, both from Sanyo. They could still be found over here. The interesting point is that they are made in China. Only the 2500 and 2700 mAh cells are still made in Japan. I guess the Eneloops will be too.


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## jtr1962 (Nov 11, 2006)

Those are interesting observations, Tom. The quest for ever higher capacities reminds me of the MHz/GHz race in the computer industry. Anyone familiar with microprocessors knows that a faster clock speed doesn't necessarily correlate with faster day-to-day operation. There are lots of other underlying variables. Unfortunately, the average person on the street thinks a 3GHz machine is better than a 2GHz one so the computer manufacturers aim for higher clock speeds instead of more operations per clock cycle. However, a distinct disadvantage of these higher clock speeds is more heat and more complex pcb design. It's only in the last year or so when physics has begun to place an inherent limit on clock speeds that we have started to use things like dual-core processors.

Rechargeable cells seem to be following a similar trend. The average person on the street knows little about self-discharge (at least until they go for a camera which has been sitting a few weeks only to find the batteries are dead) or cycle life. However, they are easily wowed by large capacity numbers. It's only now that cell capacity is approaching the inherent physical limits of NiMh chemistry that cell manufacturers have needed something else besides capacity to distinguish their cells. Hence, the low self-discharge cells like Eneloop. Interestingly, it was probably the very high self-discharge rates of the ultra-high capacity cells which created the need for cells with a lower self-discharge in the first place. And 15 minute charging has been done I suspect largely for marketing reasons as well since the marketplace needed another thing to distinguish cells other than capacity.

My take on all this is that if 2000 mAh is really the magic number for very low self-discharge then I'd rather that the manufacturers just concentrate on making such cells cheaper and better, and forget the higher capacity ones entirely until they can produce more robust, low self-discharge versions. A 2500 mAh cells which requires constant babying and only lasts 100 cycles isn't terribly useful to me. From my perspective, 2000 mAh is plenty. I remember well the days of 450 or 500 mAh AA Nicads. A cell with over four times the capacity and which retains 85% of capacity for a year is a quantum leap compared to what I used 15 years ago. If a 2500 mAh version can be made with these charactersitics, wonderful. If not, I'm more than happy with a reliable 2000 mAh cell rather than a finicky 2500 mAh one.


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## NiOOH (Nov 12, 2006)

jtr1962 said:


> If a 2500 mAh version can be made with these charactersitics, wonderful. If not, I'm more than happy with a reliable 2000 mAh cell rather than a finicky 2500 mAh one.


 
I agree 101%.


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## NiOOH (Nov 12, 2006)

In order to achieve higher capacity, the engineers had to sacrifice cycle life. It has to do with the chemical and electrochemical reactions taking place, inside a NiMH cell. I’ll try to explain why without involving too much chemistry.

The capacity of a NiMH cell is determined by the capacity (the amount) of the positive electrode, which is made of nickel hydroxide. However, there is an excess of a negative MH-alloy material inside the cell. During charging, the positive electrode becomes charged first and enters overcharge. This is accompanied with the emission of oxygen-gas from the positive electrode. This gas passes the separator and is recombined on the negative, MH electrode via a couple of chemical and electrochemical reactions. Mind that this is not yet an overcharge of the whole cell, and is necessary for the proper charging and sealing of the cell. If you look carefully at the internal pressure and temperature profiles during fast charging, you’ll see that both parameters start to increase sharply at approximately 80 % state of charge (SOC). This is exactly the point when the positive electrode is fully charged and the process of oxygen recombination on the negative electrode begins. At 100% SOC, both electrodes are fully charged and the negative electrode’s ability to recombine oxygen is decreased. The positive electrode, however, still produces oxygen at the same rate. If quick charging is not terminated, the internal pressure and temperature rise catastrophically, and the cell eventually vents. 

Now, the only way to increase the capacity of a NiMH cell is to increase the amount of the positive electrode material. Since the cell volume for a given size is the same, the way to go is to decrease the amount of material at the negative electrode. Thus, the cell’s ability to absorb overcharge is decreased. The cell is also running hotter even before reaching 100% SOC, i.e. during the recombination phase, and its average internal pressure is higher compared to lower capacity cells. The result is shorter cycle life. Another way to get some space, as Tom has pointed out, is to decrease the thickness of the separator between the positive and negative electrodes. Thus, it wears out faster due to thermal sliding, and is more prone to rupture from crystals formed at the electrodes surface. It is the wearing out of the separator that causes increased internal resistance towards the end of the cell life.
Running the capacity race, the engineers battle to use virtually every cubic micron inside a cell. This is particularly true for smaller cells, mainly AA and AAA size. Just look at the mass of the newer cells compared to older, lower capacity ones. Companies are well aware of the harmful influence this has on cycle life. It is not a coincidence that the major NiMH cell manufactureres still keep their lower capacity cells in production. Look at Sanyo, GP and Panasonic, which together hold over 90% of the market. Sanyo still makes 1700 mAh AA cells albeit in China. GP keeps its 1800 mAh cells in production. Panasonic has a 1600 mAh cells out.


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## Handlobraesing (Nov 12, 2006)

SilverFox said:


> Hello Bcwang,
> 
> Keep in mind that the results are for 100% depth of discharge cycles. I believe that if you re-charge frequently, *the actual number of cycles goes up exponentially.*
> 
> ...



Perhaps. The charge manager on-board Prius keeps the battery pack below fully charged and above heavy depth of discharge. Perhaps this is the key to preserving longevity?


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## WildChild (Nov 12, 2006)

Just take a look at batteries used in wireless phones. All NiMH are below 1600 mAh, probably because they are more robust.


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## NiOOH (Nov 12, 2006)

WildChild said:


> Just take a look at batteries used in wireless phones. All NiMH are below 1600 mAh, probably because they are more robust.


 
..and cheaper too


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## SilverFox (Nov 12, 2006)

I just remembered that the Ray O Vac IC3 15 minute charger was packaged with 2000 mAh cells.

I think the first batch of Energizer 15 minute chargers were supplied with 2200 mAh cells.

I was checking around and there are still some 2000 mAh cells available (other than the Eneloop cells). I may have to pick some up and see if they are any good.

The self discharge rate on normal 2000 mAh cells is lower than the higher capacity cells, so I wonder how they compare to the Eneloop cells...

A new round of self discharge testing may be in the works...  

Tom


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## NiOOH (Nov 12, 2006)

Tom,

Here in Europe there are plenty of lower capacity cells to be found, from Sanyo, Panasonic, GP and Varta.


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## WildChild (Nov 12, 2006)

I guess it's only a matter of preference and needs. I think most people don't even know and care about batteries with more capacity dying after 100 cycles. If they go for a trip, they probably want to charge less often so capacity is better. Also, they probably don't care about fast charging killing batteries earlier because people are always in a hurry when they need something so for them faster is better. If it die, they will only replace it not thinking how many cycles they did before it happened. Anyway, about 15 cycles is enough to cover the price of buying only alkaline batteries. Every cycles after this is money saved. 

But, there is still a market for strong batteries that won't die too early. A lot of devices that need rechargeable batteries are made so it should be replaced as late as possible (electric razor, wireless phones). These devices still use NiCd or low capacity NiMH because they are stronger and last longer, even if they have a lower capacity. People don't care about the time their telephone will last before needing to be charged again, they will probably charge it at night or every 2-3 days and it will always be OK for them. If the Eneloop are really what Sanyo said, I think they are probably the best of both world. Batteries that have enough capacity, that will last longer than higher capacity ones and that have a very low self discharge rate for NiMH! They shouldn't push them for more capacity and keep them excellent like they are. Based on SilverFox tests, they are able to sustain high current (10A) while keeping voltage, they seems really good like Sanyo said with their low self discharge rate and they probably handle more cycles than high capacity one. 

All this is based on my point of view! I will still keep some high capacity batteries even if they are weaker and I will still use my Energizer 15 minute charger because I don't always have time to wait for batteries to charge. Now, I'm waiting some Eneloop to test them. I'm pretty sure I will enjoy them. Also, I have seen 8 Energizer 2500 mAh batteries die because they self-discharged in about 1 week, and this after only 4-5 cycles and this show that it is probably more difficult to make high quality product while trying to push the limits. I also have some Sanyo 2500 mAh and some Duracell 2650 mAh batteries that have yet to show signs of high self-discharge after maybe 10 cycles each. If they discharge by themselves in about 1 month, I probably will never notice it because it often takes me less than this time to use them.

As a final word, like I said, there will always be a market for high capacity NiMH and lower capacity ones that are stronger and will last longer. Both kind should always be made by manufacturers if they want to do money and everyone to be happy!


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## bob_ninja (Nov 13, 2006)

Yeah, but the trouble is the lacking this knowledge I used to assume that higher capacity batteries can supply more power at a higher rate (just a common sense, which doesn't work all the time 
I simply assumed that a 2.5Ah Energizer can provide far more power at a high rate (high current draw) than a smallish 0.7Ah NiCd. Of course, now I know better, but I was puzzled for some time beforehand.

I have a couple of cats and a 1 year old kid, so my dustbuster is very busy  After its NiCds died I modified it to use AAs. At first I used Energizers 2.5Ah, then tried Sanyos 2.5Ah. It just didn't work well at all and batteries didn't last. Then I tried 0.8Ah NiCd and wolla, works like a champ but didn't last. After reading this forum I tried 2Ah batteries the other day. Some are older some are brand new, not even broken in yet. Again, works great albeit short run time (because of the new batteries that I need to break in)

So seems to me 2Ah are far more robust. Sure I'll keep using 2.5Ah ones as well for lower draw applications. However, it is good to know that they suck. I just don't want to waste my time trying to figure out which high capacity NiMH collapsed because a device may draw a lot of current. Before I kept finding a 2.5Ah Energizer dropping to 0V. Indeed, I found new 2Ah batteries on sale (local Canadian brand) so they are still sold.

Anyway interesting reading and thanks to all for great info


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## LightBright (Nov 14, 2006)

Thanks Silverfox for your efforts and posting your test results. It was casually mentioned that recharging or topping off WAY before the cell was out of juice was one way to extend the life of the cell, is that correct?

I revived a Dustbuster myself - I tested the motor's current draw (~3.7VDC at 9, yes NINE AMPS) and installed 6 Lithium Ion cells. It works great!


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## bob_ninja (Nov 14, 2006)

LightBright,
9 amps ) ) WOW
I did suspect that it draws a lot. I have 8 AAs replacing 6 Cs. That is about 1 amp per AA. So far my 2Amp NiMH batteries do handle fairly well. Thanks for the info


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## Ergolator (Dec 4, 2006)

Silverfox,

This is the best test data and analysis that I have been able to find regarding the effect of "fast" 15 minute chargers on cell life. It inspired me to perform my own testing on the cell temperatures reached on the Energizer CH15MN charger.

I monitored the cell temperature of the four brands of AA NiMH cells listed until the fan on the CH15MN went off. The first peak was reached when the LED on the charger switched from red to green. The testing was terminated when the fan on the CH15MN went off.

Interesting to note is the second temperature peak on most of the cells after the LED had already switched to green. 







Note: The Energizer cells tested at greater than 2500mah capacity even though they are labelled 2200mah. Maybe this is the Energizer 2500mah cell derated for the partial charge in the "fast" charger??

Thanks for the great data.

-Jerry


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## SilverFox (Dec 5, 2006)

Hello Jerry,

Very interesting...

It is good to see that the cells are staying below 50 C. I am not sure of the reason for the double hump.

Tom


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## altis (Dec 5, 2006)

If I read the description correctly, the first hump coincides with the LED turns from red to green. This is probably the end of the fast charging. Then the charger probably switches to top-off mode and the current drops significantly. As the cells get properly full the temperature rises again until the charger stops completely or switches to trickle mode.


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## SilverFox (Dec 5, 2006)

Hello Altis,

I don't believe the Energizer 15 minute charger has a top off mode. It does have a 100 mA trickle charge, but in roughly 8 minutes, that would only account for around 13 mAh. Perhaps they have changed to include a top off stage...

Tom


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## wptski (Dec 5, 2006)

Ergolator said:


> Silverfox,
> 
> This is the best test data and analysis that I have been able to find regarding the effect of "fast" 15 minute chargers on cell life. It inspired me to perform my own testing on the cell temperatures reached on the Energizer CH15MN charger.
> 
> ...


Jerry:

Somewhere are my posts showing the charge cycle of the E-15. It actually stops charging for a minute or so and rssumes at about half of the max current. The strange thing which I've yet to figure out is that this second stage is skipped at times and it doesn't repeat itself on the same cell again!


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## Ergolator (Dec 5, 2006)

Hi Bill,

Thanks, I was unaware of the half current mode. That would go a long way toward explaining the second temperature peak in the data which is certainly due to a much higher average current than the 100ma trickle charge seen at the end of the test with the cell temps below 30C.

My testing would suggest (at least on some of the cells) that the charger stops charging for about 4 to 5 minutes before resuming at the half current level. Also it is interesting that you cannot repeat the charge profile with the same cell...a variable yet to be isolated.

More clues to ponder.

-Jerry


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## Ergolator (Dec 5, 2006)

Bill, 

I found your time domain data for the E-15 charge profile - very cool. I see exactly what you meant by the half current mode. This certainly must correspond to the second temperature peak in my measurements.

-Jerry


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## Ergolator (Dec 6, 2006)

Hi Tom,

The average current output of the charger is controlled by adjusting duty cycle of the charger’s 7.5 amp maximum output. The following chart combines the cell temperature profile with the cell charging current. There are three distinct phases in the charging process.

Phase 1: High current. The duty cycle in this phase is close to 100%. This phase begins with charge initiation and ends when the LED changes from red to green. This is where the first temperature peak occurs.

Phase 2: Mid Current. The duty cycle in this phase is around 50% and was coined by Bill as the “half current” phase. This phase begins when the LED changes from red to green and ends when the fan turns off. This is where the second temperature peak occurs. This phase is important because it shows that the cells are not fully charged when the LED turns green. A significant portion of the charge occurs after the LED has turned green.

Phase 3: Low Current or trickle charge. The duty cycle in this phase is very low (I calculate 1.3%) to obtain the 100mA trickle current. This phase continues for 24 hours or until the cell is removed or the power is turned off.








A cell profile with a more pronounced second peak is hown here:





-Jerry


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## SilverFox (Dec 7, 2006)

Hello Jerry,

I believe the Duracell 15 minute charger uses the same algorithm. It seems a little less aggressive, and may have a shorter bulk charge, and a longer half charge cycle.

By the way, the Energizer 15 minute charger only continues the 100 mA trickle charge for 24 hours, then it shuts off.

Tom


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## Ergolator (Dec 7, 2006)

Hi Tom,

Thanks for the information on the 100ma trickle charge cut off after 24 hours - so corrected in my post.

-Jerry


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## Handlobraesing (Dec 7, 2006)

Anyone else's Sanyo 2.7Ah or Duracell 2.65Ah batteries substantially losing capacity or developing self-discharge rapidly?

Mine were excellent when new. Only after a few tens of charging, capacity seems to go down with every charge with two cells now down to 1.9Ah and they self discharge like crazy now.


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## WildChild (Dec 7, 2006)

Handlobraesing said:


> Anyone else's Sanyo 2.7Ah or Duracell 2.65Ah batteries substantially losing capacity or developing self-discharge rapidly?
> 
> Mine were excellent when new. Only after a few tens of charging, capacity seems to go down with every charge with two cells now down to 1.9Ah and they self discharge like crazy now.



It seems people had problems with high self-discharge with Sanyo 2.7 Ah. I didn't charged my Duracell 2650 mAh for enough cycles to see any problem for now... I hope Duracell will still exchange them if there is again a problem with those! I wish Duracell sold low self-discharge NiMH with lower capacity! I would jump of them...

What is crazy self-discharge rate for you? I had a bad batch of Energizer 2500 mAh self-discharge within 6-7 days.


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## Ergolator (Dec 8, 2006)

WildChild said:


> What is crazy self-discharge rate for you? I had a bad batch of Energizer 2500 mAh self-discharge within 6-7 days.


 
I have some Energizer 2500 mah cells that are almost as bad.

1 day - Down 12% of actual capacity
5 days - Down 21%
12 days - Down 30%
30 days - Down 63%

I have some Chicago electric (Harbor Freight) 2000mah cells that I plan to check to see if there is significant improvement at the lower capacity.

-Jerry


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## bfg9000 (Dec 10, 2006)

Great work, Tom! Is your CBA's 2.5A discharge through a resistor or a pulsed regulator to arrive at an averaged constant-current? I ask because there is one other thing that may theoretically affect cycle life greatly--the load profile:


batteryuniversity said:


> ...nickel-metal-hydride exhibits a reduced cycle life when powering a digital load.
> 
> In a recent study, the longevity of nickel-meal-hydride(sic) was observed by discharging with analog and digital loads to 1.04V/cell. The analog discharge current was 500mA; the digital mode... ...applied 1.65-ampere peak current for 12 ms every 100 ms and a standby current of 270mA..
> 
> With the analog discharge, the nickel-metal-hydride provided an above average service life. At 700 cycles, the battery still provided 80% capacity. By contrast, the cells faded more rapidly with a digital discharge. The 80% capacity threshold was reached after only 300 cycles. This phenomenon indicates that the kinetic characteristics for the nickel-metal-hydride deteriorate more rapidly with a digital rather than an analog load.


 This leads to an interesting question: do PWM regulated lights decrease NiMH cycle life? And I wonder if battery charger/analyzers like the Cadex, BC-900 or MH-C9000 use resistor banks or digitally pulse a load into a fixed resistor. I'd guess the latter to conserve space and economize on 5w resistors...

I have now had 16 bad Energizer 2500s that self-discharged to <1.0v in <4 weeks. They may well have been too easily damaged by impact (I am treating the replacements much more gently) or from overcharging (I found the charger I used terminated at 1.55v, yuk), which would make the usual separator wear-out issue a moot point. But at least we now know that fast-charging in itself isn't particularly bad, though it would sure be nice to know if we could expect better than 150 cycles with our unregulated, direct-drive lights. Maybe even the expected 300-500...


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## SilverFox (Dec 10, 2006)

Hello Bfg,

The CBA units are an analog load.

I believe on PWM lights, the pulsing comes from the converter board and effects the LED. The load on the battery is constant.

Tom


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## bfg9000 (Dec 10, 2006)

Thanks Tom!

I do know that most DC-DC switching regulator designs use either pretty large smoothing caps on both Vin and Vout (with an inductor on Vin) or a high frequency multi-phase design. The PIR1 looks to be single-phase + low frequency (for efficiency) with only a couple small tantalum caps and this thread reveals the caps on the prototype were only filtering power for the microcontroller! Since Willie Hunt's LVR is supposed to be similar (explaining Newbie's delightful contempt of it), I was wondering if anybody has actually measured the battery load profile from the A2 or PIR1?

OTOH I wouldn't expect the Hotdriver, which is a linear regulator, to put anything but a constant load on the battery. But then I only know just enough to get in trouble...


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## Ergolator (Dec 12, 2006)

bfg9000 said:


> And I wonder if battery charger/analyzers like the Cadex, BC-900 or MH-C9000 use resistor banks or digitally pulse a load into a fixed resistor.


 
bfg9000,

A very interesting find...

The BC-900 uses pulse width modulation on both the charge and the discharge functions.

-Jerry


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## B612 (Dec 15, 2006)

Does anyone know how the self discharge relates to C or D cell capacity, can the same technology be used in larger cells so could you say a 10 Ah D cell has better self discharge properties than a 12 Ah one.

I've weighed some duracell copper tops purchased at the same time and assumed a capacity of 2000 mAh for the AA cell, then divided it in to the weights for a rough guide.

AA 24.2g 2000 mAh
C 71.5g 5909 mAh
D 145g 11,983 mAh


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## LuxLuthor (Mar 23, 2007)

Tom, I'm glad you quoted this thread in the C9000 discussion. I now understand what happened to my 9 x IB-1400's. Really great work, even if it takes "noobs" like me a lot of thinking to figure it out.

:rock:


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## Led_Blind (Mar 23, 2007)

B612 said:


> Does anyone know how the self discharge relates to C or D cell capacity, can the same technology be used in larger cells so could you say a 10 Ah D cell has better self discharge properties than a 12 Ah one.
> 
> I've weighed some duracell copper tops purchased at the same time and assumed a capacity of 2000 mAh for the AA cell, then divided it in to the weights for a rough guide.
> 
> ...




Remember the casing has a bit of weight, tho when you say copper top you mean Alk right? The only numbers i know for alk's is AA's at c\20 go for about 2700ma. D's go for about 24000ma at the same rate. (i think)

The cell size should have little to no impact on self discharge. Its all about construction and chemistry.


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## knot (May 9, 2007)

Handlobraesing said:


> Tom,
> 
> 
> As an exception, they define maximum charging current for HR-4/3AU and HR-4/3FAU as 3.0A.


 Is there any flashlight use for this battery size? I bought a used 10.8V 4000mAH MiMH battery pack at a thrift store thinking there would be AA inside.


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## SilverFox (May 9, 2007)

Hello Knot,

There is not a standard flashlight that uses those size cells. I believe those are used in RC cars and trucks.

Tom


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## knot (May 9, 2007)

I have some other batteries. They are the same length but slightly larger in width - and 4 volts. Flashlight use?

**edit - I think it's a lithium battery since it's the exact same size as 18650


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## Handlobraesing (May 9, 2007)

Silverfox, the Duracell simple charger + 4AA pack contains 1800mAh batteries.


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## mdocod (May 10, 2007)

this is a really neat test you've done here.



> I often find that you set out to find the answer to a question, but during, and after, the testing, more questions come up.-Silverfox



man, is that ever true, lol. 


This thread gives me even more compelling evidence to just stick with my vanson "speedy" box. (SLOW charger). I think when need more cells, I'm thinking maybe just using cells that are designated "high current," or "low self drain," or "~2000mAh" because they all seem to go hand-in-hand.


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## HexiumVII (Jun 18, 2007)

Have you guys found the average life of NiMH regardless of cycles? Alkalines have an expiration date of about 5 years. Lithium seems to last almost double. Never seen any expiration date for rechargeables though.


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## bob_ninja (Jun 18, 2007)

*Re: Cycle Testing Observations…*

Well it is all over the place. I don't even think that battery makers give any guarantees or even estimates.
For example, many of us had to throw away Energizers after a couple of months. People keep talking about a bad batch, but then many other high capacity AAs don't last a full year.
On the other hand there was a thread about NiCds that are 10 and 20 years old. I certainly have some older NiMH AAs that are about 10 years old and still work.

The general rule seems to be that SOME lower capacity AAs that have a robust constructions (maybe like Eneloops) can last many years, over 10 years.
As an example, Toyota Prius has a massive pack consisting of C or D size NiMH cells of a very high quality. Most owners have no problems with them. The cars was introduced about 10 years ago. However, the computer controls SOC to the 20%-80% range to extend their lifespan.

So the right type of cell that us treated well can go 10+ years.


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## HarveyRich (Jun 19, 2007)

*Re: Cycle Testing Observations…*

This is a very interesting thread, that I've just read for the first time. Thanks Silverfox for starting the discussion with your excellent NiMH tests. I have a question that I don't believe was answered in the posts. It is my understanding that you can extend the life of NiMH batteries which have lost some of their charging cycles by doing a few refresh cycles on them every so often. That is doing several very slow discharges and charges tends to rejuvenate older batteries. I've had this experience using my BC-900 charger. So, wouldn't it be possible to take a battery which has lost some amp-hr and voltage capacity over time and bring it closer to original specs? Would this actually extend the life of the battery over time?

Testing batteries this way would take a lot of time and require at least two to four batteries and then run them for 100-150 cycles, refresh half of them, then run them for another 100 or so cycles, refresh the same ones and keep doing it for 500 or more cycles. The refresh discharge and charge rates would have to be very low--on the order of .1C or .2C, I think.

Harvey


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## SilverFox (Jun 19, 2007)

*Re: Cycle Testing Observations…*

Hello Harvey,

I actually did that during the second round of testing, and I don't believe it helped at all.

I have tried a variety of methods to try to get the Sanyo cells back to normal performance, but have had no luck. 

The main purpose of the slow charge and discharge is to redistribute the electrolyte within the cell, and allow the separator and electrodes to absorb it. Electrolyte starvation is usually a result of storage, or partial charges. I was going through several full cycles each day, so I don't think the slow charge would be beneficial in this case.

I think I just wore them out.

Tom


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## radellaf (Jan 10, 2008)

jtr1962 said:


> ...thinks a 3GHz machine is better than a 2GHz...Rechargeable cells seem to be following a similar trend. The average person on the street knows little about self-discharge (at least until they go for a camera which has been sitting a few weeks only to find the batteries are dead) or cycle life. However, they are easily wowed by large capacity numbers.



IOW, if we combine the laments here and and on dpreview, we will have 30mpixel pocket cameras with 4Ah batteries that will take a 1000 photos of pure noise for a couple of hours before the batteries die, whether or not the camera is being used.


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## SilverFox (Apr 17, 2008)

Update:

I have started another round of cycle testing.

Since Eneloop cells have become very popular, and there have been some discussions on fast versus slow charging of them, I decided to see what the effect of fast charging on them is.

I have modified the test procedure, a little, to single out the effect of fast charging.

With this test I am charging on the Energizer 15 minute charger, until the fan stops. I then rest the cells for 30 minutes before discharging them. This time, I am using a 1 amp discharge rate. I don't think a 1C discharge rate is hard on a cell, but by limiting the discharge rate to 0.5C, I can minimize this variable.

Other than the change in discharge rate, this test will be very similar to the test using the Titanium 2000 mAh cells.

Does anyone care to venture a guess on what will happen?

I will give you a hint... after the first 25 cycles, the capacity of cycle 25 was about 99% of the capacity of cycle 1.

Tom


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## Black Rose (Apr 17, 2008)

SilverFox said:


> Does anyone care to venture a guess on what will happen?
> 
> I will give you a hint... after the first 25 cycles, the capacity of cycle 25 was about 99% of the capacity of cycle 1.


Impressive.

Assuming the cells lose capacity in a consistent fashion (1% every 25 cycles), it would take 500 cycles for them to lose 20% of the cycle 1 capacity.


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## Anders (Apr 17, 2008)

Hello Tom.

Interesting....

I think they will hold their charge until........cycle 160.

Anders


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## tino_ale (Apr 17, 2008)

Can't wait to see the results. The tests you are making is an awesome addition to CPF shared knowledge about batteries :twothumbs

I'm beginning to play with my newly acquired CBA but I don't have the time or equipment to run tests like you do. I'm still very happy of this tool to find out the health of the cells I own and determine how they behave under different loads.


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## SilverFox (Apr 19, 2008)

50 cycles and still going strong...

Tom


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## BentHeadTX (Apr 20, 2008)

SilverFox said:


> 50 cycles and still going strong...
> 
> Tom



Thanks Tom 
I recommend Eneloops to everyone that does not recharge their cells every day. Good to hear they can handle a beating and still put out great specs after 50 cycles. 90% of what I use runs Eneloops and I am still happy with them almost a year later. Keep up the good work and I am really interested in the 100 cycle test.


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## mighty82 (Apr 28, 2008)

Great work!! How many cycles have you put the eneloops through now? 
When you are done testing them, maybe you can put them away for a month or two to see if they still have the low self discharge. That's what i'm most interested in knowing.


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## Black Rose (Apr 28, 2008)

mighty82 said:


> Great work!! How many cycles have you put the eneloops through now?
> When you are done testing them, maybe you can put them away for a month or two to see if they still have the low self discharge. That's what i'm most interested in knowing.


Here is the link to the Eneloop Self Discharge study that SilverFox is also doing: 
https://www.candlepowerforums.com/threads/149804

Also includes some info on the ROV Hybrids and GP Recyko cells.


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## mighty82 (Apr 28, 2008)

Black Rose said:


> Here is the link to the Eneloop Self Discharge study that SilverFox is also doing:
> https://www.candlepowerforums.com/threads/149804
> 
> Also includes some info on the ROV Hybrids and GP Recyko cells.


I know all about that. But the thing i want to know is if they have the same LSD capabilities after they have been abused and have taken a lot of cycles. This cells would be great test subjects for that.


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## SilverFox (Apr 28, 2008)

Hello Mighty,

At cycle 98 they were still going strong...

Tom


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## SilverFox (Apr 30, 2008)

Update:

The Eneloop cells are finally starting to show some signs of wear...

At cycle 100, they still have good capacity, but their watt hours had dropped to around 98% of the initial value...  

These are some very impressive cells.

Tom


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## Black Rose (Apr 30, 2008)

Only a 2% drop in watt hours after 100 cycles...that's very impressive.

After cycle 25, you indicated that they lost 1% capacity. Now at 100 cycles, has the capacity loss increased or remained stable?


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## SilverFox (Apr 30, 2008)

Hello Black Rose,

At cycle 100, they were actually at about 101% of initial capacity.

Interesting cells...

Tom


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## WildChild (Apr 30, 2008)

SilverFox said:


> Hello Black Rose,
> 
> At cycle 100, they were actually at about 101% of initial capacity.
> 
> ...



Great! I hope Eneloop will always stay like this... 2000 mAh is just a perfect round number for capacity. If they can last that many cycles and they can manage to lower the self-discharge rate, with the same capacity, I'm all in!


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## mighty82 (Apr 30, 2008)

My biggest concern is still the self discharge. Does it increase with the number of cycles? Capacity loss is easy to spot, increased self discharge is harder. So far i'm VERY impressed with this cells.


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## SilverFox (May 8, 2008)

Update:

Well, these Eneloop cells are finally starting to show signs of wear...

At 125 cycles, they are down 5% in capacity, and are down around 10% in Watt Hours. 

I think they will make it to 150 cycles without problems, but if the degradation trend continues at the same rate, I don't think they would make 500 cycles.

I am still very impressed with their performance. 

Tom


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## Mr Happy (May 8, 2008)

This is still using the Energizer 15 minute charger?


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## Black Rose (May 8, 2008)

Will be interesting to see if the end result of this test matches up closely with the Sanyo 2500 tests in post #1.


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## SilverFox (May 8, 2008)

Hello Mr Happy,

Yes.

Tom


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## mighty82 (May 8, 2008)

Have you only done testing with the 15 munutes charger this time? I guess they would last many more cycles when charged at 0.5C - 1C


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## SilverFox (May 8, 2008)

Hello Mighty,

Yes, I am only working with the 15 minute charger this time. It would be interesting to do another round using the Eneloop charger to give a slow charge reference.

These cells are holding up very well, but theoretically you should get better life from charging at 0.5 - 1.0C.

Tom


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## jayflash (May 8, 2008)

Tom, do you plan to test those quick charged cells for self discharge rate? I'm wondering whether the "beating" affected the LSD capability. Thanks.


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## SilverFox (May 8, 2008)

Hello Jayflash,

I think I could manage that. 

Tom


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## mighty82 (May 8, 2008)

I think someone told me a while back, that I should not charge NiMh cells more than 3-4 times per day. That I would get less cycles out of the cells if I charged them too often, without letting them rest. Could this have an affect on your results, or is this just bs?


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## SilverFox (May 8, 2008)

Hello Mighty,

I think this has to do with heat. If you let the cells cool off, you can do as many cycles as you want to. As it works out, I am getting around 4 cycles a day.

Tom


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## SilverFox (Jun 9, 2008)

Well, after 30 days self discharge on the cells, the effects of 15 minute charging are becoming clear.

Under a 1 amp load, the voltage of the cell dropped almost to 0.9 volts, then held for awhile. Gradually the voltage climbed to over 1.0 volt, but that was about as good as I could get. 

Normally, Eneloop cells will test at around 80% on my ZTS tester after they have been sitting for a few weeks. These cells tested at 40%.

It looks like they lost around 15% of their capacity in 30 days after all these cycles. I could probably bring them back for daily use, but if they were sitting on the shelf for any length of time, the internal resistance will go up to the point where they would be unable to hold voltage under load.

Very interesting test.

I try and get the graphs up in the first post shortly.

Tom


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## mighty82 (Jun 9, 2008)

Exacty what I was worried about. The low self discharge ability will disappear over time, especially with quick charging.


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## Black Rose (Jun 9, 2008)

What is the charge rate on the Energizer charger? 

I would guess somewhere in the 7A to 8A range in order to get a 2000 mAh cell to charge in approx 15 minutes.


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## SilverFox (Jun 9, 2008)

Hello Black Rose,

The Energizer 15 minute charger charges at 7.5 amps.

Tom


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## TorchBoy (Jun 10, 2008)

How did I ever miss this? Awesome stuff, Tom.


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## SilverFox (Jun 12, 2008)

Well... R. I. P. Eneloop test cells.

I have been trying different things with these cells, but it looks like after 150 cycles at 7.5 amp charging, they are done.

I charged them up and put them into my Cannon Powershot A540. I usually get hundreds of shots on a set of batteries, but these cells only gave me a total of 23 shots, with flash. The low battery indicator came on after 10 shots and I was able to coax another 13 shots out of them before the camera shut down and would not turn back on.

I tried to charge them in the 15 minute charger, but it rejects both cells. 

If you plan on using 15 minute charging with Eneloop cells, don't expect to get more than 150 cycles from them.

Tom


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## Mr Happy (Jun 12, 2008)

Hmmm. It seems like I will be putting away my Energizer 15 minute charger and not using it again.

To put this into context, what might be expected of other LSD cells, or perhaps the ordinary non-LSD cells that are more likely to find themselves in need of a rapid charge?


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## BackBlast (Jun 12, 2008)

Mr Happy said:


> Hmmm. It seems like I will be putting away my Energizer 15 minute charger and not using it again.
> 
> To put this into context, what might be expected of other LSD cells, or perhaps the ordinary non-LSD cells that are more likely to find themselves in need of a rapid charge?



I'm slow charge cycling an eneloop and a rayovac hybrid. I just finished cycle 177. (c9000 1A discharge/1A charge)

The Eneloop is still holding up well, it might be showing the first real signs of wear. The Hybrid started to noticeably deteriorate around cycle 130, it still works at cycle 177 but it has around 85% capacity and falling. Eneloop is still looking at >95% capacity.

I'm gonna kill these cells eventually :twothumbs


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## WildChild (Jun 12, 2008)

BackBlast said:


> I'm slow charge cycling an eneloop and a rayovac hybrid. I just finished cycle 177. (c9000 1A discharge/1A charge)
> 
> The Eneloop is still holding up well, it might be showing the first real signs of wear. The Hybrid started to noticeably deteriorate around cycle 130, it still works at cycle 177 but it has around 85% capacity and falling. Eneloop is still looking at >95% capacity.
> 
> I'm gonna kill these cells eventually :twothumbs



After 200-250 cycles on the Eneloop you should do a self-discharge test.


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## TorchBoy (Jun 13, 2008)

Mr Happy said:


> To put this into context, what might be expected of other LSD cells, or perhaps the ordinary non-LSD cells that are more likely to find themselves in need of a rapid charge?


The graphs in the first post address that, although there may be a large difference in opinion on "how bad is bad?" Are they useless when the voltage drops too much for the purpose or when the charger doesn't recognise them?


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## Mr Happy (Jun 13, 2008)

TorchBoy said:


> The graphs in the first post address that


Thanks for the reminder -- I'd forgotten about those.


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## Black Rose (Jun 13, 2008)

SilverFox said:


> Well... R. I. P. Eneloop test cells.


You should report your findings to Sanyo, they might find your test results interesting.

The fact that those cells were able to take 150 brutal charge cycles before becoming unusable is very impressive.


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## SilverFox (Jun 16, 2008)

Update:

The graph of the data from this round of testing on the Eneloop cells is now posted in the first post.

It looks like the Eneloop cells can handle about 100 charges on the Energizer 15 minute charger, then they start to fade. I think they did very well.

Tom


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## TorchBoy (Jun 16, 2008)

SilverFox said:


> Overall, I was impressed that they held up as well as they did, but for longer cycle life it would be better to keep the charge rate in the 0.5 – 1.0C range.


Now where's the graph for that? 

Thanks, Tom - great data, as always.


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## Anders (Jun 17, 2008)

Thankyou Tom for you time and effort, as usual...

Anders


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## HarryN (Jun 22, 2008)

Thanks Tom - interesting work.


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## BackBlast (Aug 9, 2008)

WildChild said:


> After 200-250 cycles on the Eneloop you should do a self-discharge test.



After 201 cycles, I did a 30 day self discharge test on the Eneloop and Hybrid cells I'm testing..

Eneloop clocked 91% capacity retention (~95% original capacity) after 30 days.
Rayovac Hybrid clocked 68% capacity retention (~87% original capacity) after 30 days.

They were in my basement, side by side, during the 30 days. I imagine a fairly consistent 65-70 degrees or so there.


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## TorchBoy (Aug 10, 2008)

BackBlast said:


> Rayovac Hybrid clocked 68% capacity retention (~87% original capacity) after 30 days.


Interesting results. Does that imply the Rayovacs lost their LSD quite quickly, or was it not there to begin with?


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## BackBlast (Aug 10, 2008)

TorchBoy said:


> Interesting results. Does that imply the Rayovacs lost their LSD quite quickly, or was it not there to begin with?



It's losing it with the cycling, I believe it starts out with ~85-90% after 30 days on a new cell. The more wear on the cell increases self discharge.


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## SilverFox (Aug 10, 2008)

Hello BackBlast,

Interesting results. Thanks for sharing.

I wonder if the increased capacity of the Ray O Vac cells has anything to do with their drop off of many cycles...

Tom


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## DynoMoHum (Dec 29, 2009)

Very interesting testing... Talk about time consuming... wow.


Now I just finished reading this whole thread, I may have missed a few points along the way... Hope this wasn't already made clear somewhere and I just missed it...

I can't tell if the cycles using the rapid charging were completed in much faster time then the cycles of the slower charging method. That is... Were the same number of cycles per time period conducted with each charge method? or were the high charge rate cycles completed in much less total time?

The reason I ask, is cause I wonder how much a lack of rest time between cycles effected the cell life, in comparison to the effects of the charge rate.

When I was racing RC cars, it was common practice to let out packs rest for a week between charges. It was thought that charging some cells more then once a week was very hard on them. Some of this changed depending on who you talked to and/or what type of cell was being used. Some types of cells were supposed to be able to be charged/used twice on a single race day, others were never used that way, and it was very rare that anyone but novices ever used the same pack more then twice a week.

When reading this thread, I noticed that the Eneloop cells seemed to have the first 100 cycles placed on them in about 10 days or so... which means they were cycled somewhere near 10 times in 10 consecutive days. I know that part of this lack of rest for the cells was in a direct effort to abuse them and/or shorten the total time required to 'see' some change in results. However I can't help but wonder if longer periods of rest between charge/discharge cycles could have effected the over all results, particularly as it relates to the comparison of 'fast' charging vs. the not so fast charging.


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## SilverFox (Dec 29, 2009)

Hello DynoMoHum,

I have also heard that under heavy use NiMh cells seem to do better when allowed to rest for an extended time between uses. The problem is that I have never been able to substantiate that under the loads I am testing at.

You will notice that I am discharging at 1C.

Heat is the main problem with NiMh chemistry. High discharge rates do a good job of heating the cells, and it is a good idea to let them totally cool down after use, but I don't think it takes a week to cool down. With the introduction of cooling boxes, I believe the attitude changed from once a week use to making sure that the cells were cool prior to charging.

The purpose of this test was to explore what happens with rapid charging. This is slightly different from running tests to explore how to optimize rapid charging, or how to optimize charging for rapid discharging at high loads.

If your "wonder" is compelling enough, feel free to run the same tests with extended rest times and report back...  

Tom


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## DynoMoHum (Dec 29, 2009)

Umm... I guess my "wonder" level isn't that great... 


As you probably know with the RC racing crowd in the Mod classes people would drain 3300 mAh packs in 4 minutes, so the drain was at a extremely high rate. The main reason people didn't run a pack twice in a day was that on the second run the 'punch' or perceived ability to produce that really high output was reduced. With really good drivers they apparently could see the differences in their lap times, particularly in the opening laps of the races. 

Several of the battery 'matchers' would also give their recommendations as to how to treat batteries, and they tended to give some indication as to if they felt you could use the packs more then once a night. Now I suppose they could potentially sell more packs if they told you only to use one each race day... 

I had always heard that it was not so much a matter of the pack cooling down, but more that the chemicals and such needed time to normalize. In fact I had frequently heard that running fans on them to cool them faster wouldn't help any. The only time I new of people using fans was in an attempt to keep the shrink wrap from melting. Either way I had always figured we were totally abusing our cells the way we used them, and I rarely used my packs more then twice a week, in hopes that they would have the maximum output on the off chance that my car would actually hook the power to the track and I could handle it all. 

Now for back yard bashing, I frequently ran packs over and over just letting them rest long enough to get cool . But then I never tried to measure the ouput levels on any of these occasions.


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## HarryJames (May 20, 2015)

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