# Why did power tools skip over NiMh batteries?



## BatteryCharger (May 30, 2010)

I have quite a few older power tools with aging NiCd batteries - batteries that were crap even when they were new. I know that many tool manufacturers are now using lithium instead....but how come they never started using NiMh when it was the king?

Or to put the question a different way - I bought an 18v drill about 2 years ago that came with a 1300mah NiCd pack. Way, way outdated before I even bought it. At this time lithium tools were just coming out and really expensive, but still, I have never noticed any that used NiMh batteries before that. The tool uses standard sub C cells...why didn't they use a more modern ~3ah NiMh battery? Is it just economics...or is there a reason? Or rather, is there a reason I shouldn't trash the NiCds and replace them with these? http://www.batteryjunction.com/tenergy-propel-4200-sc.html for ~4x the run time?!oo:

How would the self discharge for a 4.2ah NiMh sub C compare to a 1.3ah NiCd sub C? I know the NiCds are dead after about a month or two.

I use a multi voltage NiCd/NiMh "hobby" charger to charge up all my cordless tools.


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## Beamhead (May 30, 2010)

I bought a makita drill when they first introduced NiMh packs, I even bought 4 extra packs. They are garbage, I use the old Ni Cad pack if /when I use that drill. I recently picked up 2 hitachi 18v LiIon and they kick butt.


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## bulbman (May 30, 2010)

Nimh cells are more expensive and don't take as many charge/discharge cycles


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## Light Sabre (May 30, 2010)

The answer is plain and simple: NiCads and Li-Ion batteries can deliver more current than NMH's can which means more powerful cordless tools.


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## BatteryCharger (May 30, 2010)

Light Sabre said:


> The answer is plain and simple: NiCads and Li-Ion batteries can deliver more current than NMH's can which means more powerful cordless tools.


Forget about lithiums. I'm talking about before they started using them in tools. How can a 1.3ah (nominal, more like .9ah real life) NiCd deliver more current than a 3-4ah NiMh?


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## Light Sabre (May 30, 2010)

More current as in for example: NiCad 3 amps versus NMH 1.5 amp. (I have no idea what the real numbers are.)  Has nothing to do with amp hours. It's about battery chemistry and how much instanteous current it can deliver. NiCads and Lithiums can deliver more instanteous current than NMH's can. I think it is explained at Battery University if I remember correctly.


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## Ray_of_Light (May 30, 2010)

Until the introduction of Ni-MH LSD batteries, traditional Ni-MH were known to develop an increasing internal resistance over time, starting from a resistance already higher then Ni-CD battery.
For this reason, Ni-MH wasn't initially deemed appropriate for power tools.
Nowadays high current lithium battery have all the necessary requisite to replace old Ni-CD.
This notwithstanding, I have installed LSD Ni-MH in my two drills. With some simple precautions, I believe them to be more appropriate and long lasting than lithium-ion in power tools. As longs as they are not overcharged, LSD Ni-MH have the innate tendency to keep their capacity balance - and therefore packs made of them, don't self-destroy under heavy load.

Anthony


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## Bullzeyebill (May 30, 2010)

Ray_of_Light, what amp draw are your power tools pulling using your LSD's?

Bill


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## Ray_of_Light (May 30, 2010)

I have a 4.8 V power drill, using four sub-C 1,2 Ah nicads. Average current draw was 5 Amps under load, and about 15 A when the chuck was stalled.

The other drill is a 7.2 V with electronic speed control. It used six sub-C Ni-Cd of better quality, around 2 Ah capacity. I measured 7 A under load, and the electronic circuit limits the current draw when the drill is stalled.

I used Duraloops in both drills, with excellent results. I don't use anymore the original charger for the 4.8 V drill (a wall wart with transformer and full bridge rectifier, no smoothing cap) but a dedicated multicell NimH charger.

For the 7.2 Volt drill, the table charger with the charge controller is still effective.

Both drills have a much better torque now, and are available for use anytime.

Regards

Anthony


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## Ragiska (May 30, 2010)

charging nimh packs in power tools leads to dead packs in a hurry. they cannot be trickle charged like nicads, or terminated off voltage as easily as li-ion.


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## n3eg (May 30, 2010)

What size Li-ion batteries are they using in power tool batteries? Are they all 18650?


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## BatteryCharger (May 31, 2010)

Ragiska said:


> charging nimh packs in power tools leads to dead packs in a hurry. they cannot be trickle charged like nicads, or terminated off voltage as easily as li-ion.


Well, the tool MFG could provide a proper NiMh charger. Power tool chargers are notoriously horrible, and people always complain about how much replacement batteries cost....coincidence? Everybody with a few power tools should get themselves a nice universal smart charger....

I guess it's kind of like the $40 printer that comes with a $30 ink cartridge - it's not the printer they're trying to sell you...


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## ampdude (May 31, 2010)

NiCads have low self discharge and can take a whole lot of abuse. I have some NiCad devices dating back to the 90's that still work fine, noteably a flashlight and an electric shaver. They have both been run dead and left that way countless times, but they always come back for more.


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## 45/70 (May 31, 2010)

BatteryCharger said:


> ....but how come they never started using NiMh when it was the king?



I think there are two primary reasons. First, NiCd cells have a sturdier construction than NiMH cells. NiMH cells are fragile. In power tools that are used every day, as in the workplace, NiCd's hold up better to being dropped, the tool receiving impacts, and so on.

Secondly NiCd cells hold up much better to being run down and cells within packs being subjected to reverse charging. While this is not really good for NiCd cells, it pretty much kills NiMH cells in short order.

A third reason to consider, is the fact that NiCd cells generally last between 1000 and 2000 charges, as opposed to NiMH cell's 300-500. This is offset to a large degree though by the need to recharge NiCd's more often, having to more or less completely run them down each time before recharging, as opposed to being able to "top off" NiMH's, and the NiMH cell's superior capacity. Still, in the end NiCd cells will generally achieve about twice as many Watt Hours, or more, than NiMH cells, during their lifetime.

Dave


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## Battery Guy (May 31, 2010)

This journal article has a good summary of the issues with Ni-MH cells:

_Journal of Power Sources
Volume 176, Issue 2, 1 February 2008, Pages 547-554 

Progress in high-power nickel–metal hydride batteries
Peter Bäuerlein, a, , Christina Antoniusa, Jens Löfflera and Jörg Kümpersa

aVARTA Automotive Systems GmbH, Am Leineufer 51, D-30419 Hannover, Germany

Abstract
High demands to power performance, high cycle and calendar life as well can be met by NiMH batteries, making this battery system very suitable for HEV applications. The hydrogen storage alloy plays an important role with respect to power performance and life duration. Power performance and cycle life behaviour are related to each other by the electrochemical and mechanical properties of the alloy, via a more or less reciprocal relationship. In terms of power performance at medium-discharge rates, the charge transfer reaction at the hydrogen storage alloy interface was found to be crucial for the temperature-dependent behaviour of the cell, whereas at discharge rates above about 15C diffusion limitation was found especially at the negative electrode. The alloy corrosion is taking place in alkaline media, leading to the formation of surface films and a change of the chemical composition, especially in near surface regions of the alloy particles. Consecutive electrochemical cycles lead to mechanical stress and finally cracking of the alloy particles. Stability against corrosion and pulverisation on one hand and good electrochemical performance on the other hand both depend on the chemical composition of the alloy, its morphological properties and the cycling regime used._

Unfortunately, I can't attach the full article for copy write reasons.

Bottom line is that both NiCd and NiMH use essentially the exact same cathode: NiOOH. The big difference is the anode. NiCd uses cadmium (metallic cadmium in the charged state and cadmium hydroxide in the discharged state). NiMH uses an alloy that is capable of absorbing large amounts of atomic hydrogen into its crystal lattice.

The cadmium anode is extremely stable, and can be charged and discharged thousands of times with little or no degradation. Even driving the cell into reversal does little to hurt the cadmium anode (although you lose electrolyte via electrolysis when you do this, so it is not good for the cell). So for NiCd batteries, the cycle life is typically limited by the NiOOH cathode and/or loss of electrolyte over time due to electrolysis.

Metal hydride anodes are another story. The alloy slowly corrode in alkaline electrolytes, and layer of corrosion product forms on the surface, reducing the rate capability of the alloy. Also, as the alloy is cycled and hydrogen diffuses into and out off the crystal lattice, the brittle alloy is strained and eventually begins to crack. This process is commonly referred to as "pulverization". The freshly exposed surfaces of the pulverized particles begin corroding, further reducing the amount active material and the drain rate capability.

When a NiMH cell is driven into full reversal (sometimes called Stage 3 discharge), oxygen is evolved at the metal hydride electrode, and the alloy rapidly corrodes.

Corrosion of the metal hydride alloy also releases metal ions into the electrolyte. One of these metal ions, manganese, will diffuse to the separator and form a compound with potassium. This manganese/potassium compound is conductive enough to cause short circuits within the separator. This is why older NiMH cells have terribly high self discharge rates.

So the cycle life of a NiMH cell is typically limited by the metal hydride anode, which slowly corrodes and pulverizes during use. 

While a brand new NiMH cell has a high energy density and may even be able to supply more power than a comparable NiCd cell, both the power capability, energy density and self discharge characteristics of the NiMH cell degrades faster than the NiCd cell.

Cheers,
Battery Guy


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## bob_ninja (May 31, 2010)

Even NiCd die far too quickly due to 2 major problems:

- neglect = for a commercial use this is not a problem, but most of us use drills and saws once in a while. In between projects pack may sit unused for a year or more and we all know what happens then. My 1st pack I actually left in garage during winter and it didn't survive.

- cell count = for a typical pack of around 20V you need around 15 cells. I find some packs have a very good quality cells that are well balanced. Nevertheless, such a high cell count guarantees that soon some of them will reverse. Since it is extremely difficult to replace one or two cells alone, entire pack is useless.

Therefore the new Lithium cells are now replacing NiCd as they solve both problems. Especially about 3x lower cell count means less cells to go out of balance.

I actually use one of the few NiMH packs for iRobot Roomba robots (around 24V I think). They actually perform reasonably well, but all fail around the 200-400 cycle mark (rough estimate). Robot is actually programmed to seek charging base when low power. I noticed that when robot is stuck and unable to return to the base thus taking pack down to near zero SOC, then packs starts to degrade very quickly.

So NiMH work sort of Ok, but don't provide a lot of power and don't last.

The new Lithium packs should address most problems. However for now they are expensive and sold as premium product, at 2x to 4x price of NiCds.


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## John_Galt (May 31, 2010)

Huh, I had always thought that Ni-MH was more durable than Ni-Cd, and didn't suffer from the same problems. 

I thought you always had to completely discharge a Ni-Cd battery pack, or it would develop a "memory" and only retain that capacity from then on. 

Shows me what I know...


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## Chauncey Gardner (May 31, 2010)

Beamhead said:


> I bought a makita drill when they first introduced NiMh packs, I even bought 4 extra packs. They are garbage, I use the old Ni Cad pack if /when I use that drill. I recently picked up 2 hitachi 18v LiIon and they kick butt.


 
I didn't have a good experience with the Makita nimh stuff either. Combo pack, saw & drill, not cheap.

Went to nicad Ryobi & had no issues. None with the DeWalt liion combo I have either. 
But yeah, the nimh stuff from Makita was a joke. Couple strips of trim & the saw was toast, the drill would require both battery packs just to mix up a pail of paint & just barely accomplish that.

Battery Guy & Bob ninja both had good posts. Appreciate the info above & have had similar experiences like Bob's.
The newest cordless combo I just picked up should last much longer & will not spend winter in the garage.

Good thread.


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## alpg88 (May 31, 2010)

BatteryCharger said:


> Forget about lithiums. I'm talking about before they started using them in tools. How can a 1.3ah (nominal, more like .9ah real life) NiCd deliver more current than a 3-4ah NiMh?


 
i took apart many cordless drills batteries.
not once i,ve seen 4ah nimh, the biggest nimh i,ve seen , that was btw total garbage, was 3ah.
good tool makers, like dewalt milwaukee, makita, use sub c, sanyo nicd, rated 2 -2,4ah, other cheap knock off tools use, 4\5 sub c 1,2-1,9ah. usually no name crappy cells.


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## Battery Guy (May 31, 2010)

John_Galt said:


> Huh, I had always thought that Ni-MH was more durable than Ni-Cd, and didn't suffer from the same problems.
> 
> I thought you always had to completely discharge a Ni-Cd battery pack, or it would develop a "memory" and only retain that capacity from then on.
> 
> Shows me what I know...



The infamous "memory" or voltage depression effect is caused by the cathode (positive electrode), which is the same in both Ni-Cd and Ni-MH cells. 

In general, Ni-Cd is a more robust chemistry than Ni-MH.

Cheers,
Battery Guy


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## Mr Happy (May 31, 2010)

"_Power performance and cycle life behaviour [of NiMH batteries] are related to each other by the electrochemical and mechanical properties of the alloy, via a more or less reciprocal relationship."_

Paraphrasing that sentence:

Higher Power = Shorter Cycle Life
Longer Cycle Life = Lower Power

How about that?


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## fyrstormer (May 31, 2010)

BatteryCharger said:


> Forget about lithiums. I'm talking about before they started using them in tools. How can a 1.3ah (nominal, more like .9ah real life) NiCd deliver more current than a 3-4ah NiMh?


Current is rate of flow of electric charge. NiCads cost nothing to make and they can dump charge more than fast enough to run power tools, whereas Li-Ions cost a lot to make and have a nasty tendency to explode when discharged too quickly. Also, Li-Ions hate being run dry, whereas NiCads require it, which makes them much more amenable to job-site use.

Keep in mind, if you're shopping for a power drill so you can put up some crown molding in your bedroom, you are not who the power tool companies care about -- they care about contractors who buy their tools buy the dozen and beat them to death within a year, and NiCads are what work best for that target demographic.

If only there were a website called PowerToolForums.com, or something totally off-the-wall like that rolleyes, maybe there would be a small group of custom designers there who could build you a titanium-bodied cordless drill with a DC brushless motor and spiral-cut drive gears and a zillion settings controlled via an LCD touchscreen -- and of course a lithium-polymer battery pack. But it would probably cost $2500, and _nobody_ will _ever_ in a million years spend that kind of money on a _hand tool_.


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## Mugrunty (May 31, 2010)

Just to add some info. I found this little site very informative with various Ni-cd stuff...including "memory". http://www.repairfaq.org/ELE/F_NiCd_Battery.html

I have some old GE Ni-cd packs from 1981 that still work great! They are 7.2V packs consisting of AA cells of 450mAh. Their internal resistance is up there...about 0.3 - 0.4 ohms for the entire pack. One _cool_ thing about Ni-cds is that their charging chemical reaction is strongly endothermic. The joule heating and endothermic charging sort of balance each other out...allowing for very quick charges without any heating. Once the cell approaches 100% SOC, the charge acceptance decreases...and the cell starts to heat up due to the generation and recombination of oxygen. Ever notice how a lot of those drill chargers use a temperature sensor?

I've been charging those ancient 1981 Ni-cds at 4C and they barely get lukewarm, and only towards the end of charge. I guess it depends on the quality of the Ni-cds as well. My professor had an entire box of them that were donated to the school. I'm amazed they still work at all!


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## TakeTheActive (May 31, 2010)

John_Galt said:


> ...I thought you always had to completely discharge a Ni-Cd battery pack, *or it would develop a "memory" and only retain that capacity from then on*...


AFAIK, the "memory" problem with NiCDs was explained very nicely in a NASA document where a satellite in a fixed rotation around a planet, in and out of the sun rays, DISCHARGED and then CHARGED the *EXACT* same amount in each NN (24?) hour period. If *EITHER* the daily DISCHARGE or the CHARGE were different, there would be no "memory" effect.



fyrstormer said:


> ...*Keep in mind, if you're shopping for a power drill so you can put up some crown molding in your bedroom, you are not who the power tool companies care about* -- they care about contractors who buy their tools buy the dozen and beat them to death within a year, and NiCads are what work best for that target demographic...


IMHO, this equates very closely to the folks that want to buy 10,000mAh D cells where 2000mAh AAs in adapters would work just as well if not better. If you can use up 10,000mAh in a week or less, go for the $$$ D cells (AND charger!). Otherwise, AAs will be more cost-efficient.

If you're going to use a power drill once or twice a year, you CERTAINLY don't need a cordless one! DAILY, or at least a few times a week, maybe...


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## alpg88 (May 31, 2010)

fyrstormer said:


> Keep in mind, if you're shopping for a power drill so you can put up some crown molding in your bedroom, you are not who the power tool companies care about


 
that is exactly what i had when i bought my old appt. crown moldings installed with Sheetrock screws, plus the fact that concept of leveled lines were not known to them. whoever did that should really not do any home improvements ever again. i spend 3 days ripping them off, spackle, and mount new moldings the right way, with a level, and a nail gun.


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## gSPIN (Jun 1, 2010)

not to discount any of NiMH longevity shortcomings while of valid concern to the end-user, to a tool manufacturer that is actually a bonus to sell more batteries.
put urself in the mindset the manufacturer, their overriding concern is price/performance.
where can they score the best $/Wh, same as the rest of us.

every single consumer size NiMH cell produced in the world (eneloops included) has to pay a patent royalty to Chevron (or at least did until recently when some of the patents got sold to Bosch/Samsung JV).
and that's on top of a license fee to be authorized to manufacture them.
this puts NiMH at a significant price disadvantage compared to both NiCd & Li cells that can be produced generically by just about anyone in China.

as usual, u just have to follow the money.
the other problems, (if a factor at all) were probably just the icing on the cake.
but if that's all it was i'm sure there would be lotsa companies that would be perfectly happy to continue selling crap (which i don't think the current NiMH is).


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## BatteryCharger (Jun 1, 2010)

fyrstormer said:


> If only there were a website called PowerToolForums.com, or something totally off-the-wall like that rolleyes, maybe there would be a small group of custom designers there who could build you a titanium-bodied cordless drill with a DC brushless motor and spiral-cut drive gears and a zillion settings controlled via an LCD touchscreen -- and of course a lithium-polymer battery pack. But it would probably cost $2500, and _nobody_ will _ever_ in a million years spend that kind of money on a _hand tool_.


Oh, you HAD to go and say it! I've already got seven drills...that doesn't mean I don't need more. (right?) :duh2:

That's interesting about the cycle life being longer with NiCd, I wasn't aware of that. All I know is most of the cheap NiCd tool packs I've had over the years never lasted very long nor did they have a good shelf life. I guess a lot of that has to do with the fact that I buy cheap tools. :laughing: The 12v, 4.5ah NiMh battery packs on my X990 each lasted about 300-400 full cycles, I thought that was pretty good.

I just found my old Craftsman 7.2v "Versapak" drill...my very first cordless...seems like a perfect candidate for some Duraloops. The NiCds died like 10 years ago...



gSPIN said:


> every single consumer size NiMH cell produced in the world (eneloops included) has to pay a patent royalty to Chevron (or at least did until recently when some of the patents got sold to Bosch/Samsung JV).
> and that's on top of a license fee to be authorized to manufacture them.


Wow! I was never aware of that. So Chevron invented NiMh batteries?


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## BatteryCharger (Jun 1, 2010)

In the end....would you say a battery geek like myself, with current technology NiMh and a good charger, would be better off with 4-6ah NiMh sub Cs or ~2ah NiCds in an 18v power tool pack? If I see 300 or more full cycles out of any technology I'd be happy.


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## Ray_of_Light (Jun 1, 2010)

Battery Guy said:


> The infamous "memory" or voltage depression effect is caused by the cathode (positive electrode), which is the same in both Ni-Cd and Ni-MH cells.



Check this out:

http://data.energizer.com/PDFs/nickelmetalhydride_appman.pdf

Page 14:

Memory/Voltage Depression
The issue of "memory" or voltage depression has been a concern for many designers of
devices, using nickel-cadmium cells. In some applications where nickel-cadmium cells
are routinely partially discharged, a depression in the discharge voltage profile of
approximately 150 mV per cell has been reported when the discharge extends from the
routinely discharged to rarely discharged zones. While the severity of this problem in
nickel-cadmium cells is open to differing interpretations, the source of the effect is
generally agreed to be in the structure of the cadmium electrode. With the elimination of
cadmium in the nickel-metal hydride cell, memory is no longer a concern.

-------------------------------------------------------------------

Anthony


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## Battery Guy (Jun 1, 2010)

Ray_of_Light said:


> Check this out:
> 
> http://data.energizer.com/PDFs/nickelmetalhydride_appman.pdf
> 
> ...



Looks like we are going to have the battle of dueling references. While I respect the good folks at Energizer, and think that they put out great data sheets, this particular piece of information is just plain wrong. It has been pretty well established that the memory effect is due to phase transformations in the NiOOH material. There are numerous articles on this phenomenon, the most recent by Robert Huggins at Stanford, is shown below. I can produce others if this is not convincing.

Journal of Power Sources
Volume 165, Issue 2, 20 March 2007, Pages 640-645 

Cause of the memory effect in “nickel” electrodes
Robert A. Huggins, 

Department of Materials Science & Engineering, Stanford University, Stanford, CA 94305, United States

Abstract
Several types of commercial batteries employ the H2NiO2–HNiO2 (or Ni(OH)2–NiOOH) reaction in their positive electrodes. Such batteries often exhibit a so-called “memory effect” in which the available capacity at useful voltages noticeably decreases if they are used under conditions in which they are repeatedly only partially discharged before being recharged. However, if such cells are deeply discharged, the apparently lost capacity can be recovered. It is shown that these phenomena can be rationally explained by considering the reactions in the “nickel electrode” in terms of the thermodynamics of the ternary H–Ni–O system.

And from Chapter 29- Portable Sealed Nickel Metal Hydride Batteries from the 3rd edition of the Handbook of Batteries, 2002:

29.4.9 Voltage Depression (Memory Effect)
A reversible drop in voltage and loss of capacity may occur when a sealed nickel-metal
hydride battery is partially discharged and recharged repetitively without the benefit of a full
discharge. This is illustrated in Fig. 29.13. After an initial full discharge (cycle 1) and charge,
the battery is partially discharged (in this example to 1.15 V) and recharged for a number
of cycles. During this cycling the discharge voltage and the capacity drop gradually (cycles
2 to 18). On a subsequent full discharge (cycle 19) the discharge voltage is depressed compared
to the original full discharge (cycle 1). The discharge profile may show two steps, and
the cell does not deliver the full capacity to the original cutoff voltage. This phenomenon is
known as voltage depression. At times it is referred to as ‘‘memory effect,’’ as the battery
appears to ‘‘remember’’ the lower capacity. The battery can be restored to full capacity with
a few full discharge-charge cycles, as illustrated in Fig. 29.13 (cycles 20 and 21).
The voltage drop occurs because only a portion of the active materials is discharged and
recharged during shallow or partial discharging. The active materials that have not been
cycled change in physical characteristics and increase in resistance. The active materials are
restored to their original state by the subsequent full discharge-charge cycling.
The extent of voltage depression and capacity loss depends on the depth of discharge and
can be avoided or minimized by discharging the battery to an appropriate end voltage. The
effect is most apparent when the discharge is terminated at the higher end voltages, such as 1.2 V per cell. A smaller loss occurs if the discharge is cut off between 1.15 and 1.10 V
per cell. Discharging to an end voltage below 1.1 V per cell should not result in a significant
voltage depression or capacity loss on the subsequent discharges. Discharging to too low an
end voltage, however, should be avoided, as discussed in Sec. 29.4.6.
The effect is also dependent on the discharge rate. To a given end voltage, the depth of
discharge will be less on discharges at the higher rates. This will increase the capacity loss
as less of the active material is cycled.
While the memory effect may result in reduced battery performance, the actual voltage
depression and capacity loss are only a small fraction of the battery’s capacity. Most users
may never experience low performance due to this behavior of the sealed nickel-metal hydride
cell. Often memory effect is used incorrectly to explain a low battery capacity that
should be attributed to other problems, such as inadequate charging, overcharge, or exposure
to high temperatures.

Cheers,
Battery Guy


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## gSPIN (Jun 1, 2010)

Battery Charger said:


> So Chevron invented NiMh batteries?


no, they basically bought out the company that did invent it, ECD Ovonics, via some slightly underhanded tactics (some would say) by using GM as a front.
wiki has a write up on it, even tho the article is about automotive size NiMH the last half summarizes the COBASYS (Chevron Ovonics BAttery SYStems) history fairly well.
http://en.wikipedia.org/wiki/Patent_encumbrance_of_large_automotive_NiMH_batteries

"The modern nickel-metal hydride (NiMH) electric vehicle battery was invented by Dr. Masahiko Oshitani, of the GS Yuasa Corporation, and Stanford Ovshinsky, the founder of the Ovonics Battery Company."

there is one thing left out of the wiki entry that i would add.
the article only skirts around it without clearly spelling out specifically what is the patent encumbrance.
did u ever wonder why hybrids like the Prius & Honda Insight use hundreds of rinky-dink D-cells instead of F, M or even bigger?
the amp-hour figure i've seen bandied about is that allegedly 10 Ah is the limit Chevron imposed as the max capacity cell a licensee is allowed to produce.
there are some exceptions who signed agreements prior to the Chevron takeover (Saft for one) so u do see the odd 13-15 Ah F-size.
however even to date altho the latest Prius' packs may no longer come in the D-cell form factor, at 6.5 Ah/cell it's essentially a physical prismatic repackaging of a D's capacity.

in a nutshell, except for the smallest sizes (subC & under) NiMH has essentially been held stagnant for nearly a decade.
COBASYS r&d ground to a halt after the takeover & Chevron sued Panasonic several times over winning in each case, sending a clear message preventing anyone else from developing NiMH any further.
the evidence that NiMH could be/should be much higher capacity right now than what were allowed to have is readily mathematically demonstrated.

back in the old days of the the original NiCd, standard AA capacity was 0.5 Ah & a NiCd D came in at 4.0 Ah.
those were the classic size/capacity figures that remained that way for decades.
that established a volumetric energy capacity ratio of 8:1 in going from AA to D.
mulitply that by even the supposed LSD "reduced" capacity 2.0 Ah of an AA eneloop.
or without pushing the envelope by scaling up Sanyo's 2.7 Ah super lattice, instead go with the conservative 2.5 Ah non-LSD.
it's reeely hard not to believe that 15 Ah LSD & 20+ Ah regular NiMH D-cells should be possible.
now that the first of the patents are expiring in 2010 with the rest by 2014 i'm hoping that this announcement from Ovonics will become reality from even generic battery producers.
perhaps then NiMH may prove the cheaper alternative & we'll start seeing them in power tools yet.

"In October 2009, ECD Ovonics announced that their next-generation NiMH batteries will provide specific energy and power that are comparable to those of lithium ion batteries at a cost that is significantly lower than the cost of lithium ion batteries."


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## Ray_of_Light (Jun 1, 2010)

Crystallographic studies conducted with X-ray mulecular diffraction are clarifying the previously unknown behavior of nickel superoxydes. 
One of the most important outcomes of these researches has been the tabling of yttrium dosage in LSD batteries.
It seems that, under some conditions, nickel superoxydes can built their own lattice structure. Practically speaking, if you run continously a non-LSD battery for 50 or more cycles from hot-off-the-charger straight to device, you may modify the structure of the nickel electrode - so the battery has an higher OCV and higher capacity. 
In LSD batteries, this effect is almost non-existant, since the production of higher states of oxydation of the nickel is limited by design.

This effect is not documented and, if documented, is confused with the memory effect caused from progressive surface activation typical of the cadmium in Ni-CD batteries.

I mean, during the charge of Ni-CDs, the activation of cadmium surface progresses from the areas already activated; in partial cycling, it is always the same area which participates to the active reactions, while the non-used area becomes non-responding and creates a voltage depression.
This behaviour is typical of the cadmium, it doesn't happen with the hydrogen-storing alloy of Ni-MH batteries. 

The reference available on these effects are at least a decade old. In a today academic environment, if you state that the memory effect is caused from nickel, you may lose some of your credibility.

Regards

Anthony


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## Battery Guy (Jun 1, 2010)

Ray_of_Light said:


> The reference available on these effects are at least a decade old. In a today academic environment, if you state that the memory effect is caused from nickel, you may lose some of your credibility.



With respect to credibility, I would respectively disagree that academics today refute that the memory effect is caused by the positive (aka nickel) electrode.

Again, I would encourage you to read the recently published book by Prof. Huggins from Stanford. Pertinent excerpts from which are given below. I would hardly question Prof. Huggins credibility when it comes to battery materials.

I will search for those references that talk about the cadmium electrode being the source of the "memory effect". 

_*Book: Advanced Batteries: Material Science Aspects by Prof R.A. Huggins, Stanford, 2008

Section 11C: Cause of the Memory Effect in "Nickel" Electrodes, pages 226-234
*
Excerpts: 
"It is often found that batteries with "nickel" positive electrodes, e.g. Cd/Ni, hydride/Ni, Zn/Ni, Fe/Ni and H2/Ni cells, have a so-called memory effect, in which the available capacity apparently decreases if they are used under conditions in which they are repeatedly only partially discharged before recharging."

"The phenomena that take place in such electrodes have been studied by many investigators over many years, but no rational and consistent explanation of the memory effect related to "nickel" electrodes emerged until recently. Although it has important implications for the practical use of such cells, some of the major reviews in this area do not even mention this problem, and others give it little attention and/or no explanation"

"Conclusions: The basic mechanisms that are involved in causing the memory effect have been identified. The key element is the formation of an amorphous HNi2O3 phase upon overcharging into the potential range where oxygen is evolved. Upon subsequent reduction, the presence of this phase produces the potential plateau at about 0.8 V vs. hydrogen, reducing the available capacity at the normal higher reduction potential. The more the overcharge, the more HNi2O3 that is formed, and the longer the lower plateau. If the electrode undergoes further reduction this phase disappears, and the potential drops to a much lower value. Subsequent charging of the electrode brings the composition back to the initial state, and the memory effect is cured."
_
Again, I would be happy to read any references that either refute this or provide a basis for the cadmium electrode being the source of the memory effect.

Cheers,
Battery Guy


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## alpg88 (Jun 1, 2010)

zapping fixes nicd's, not to like new stage, but to a lot better than before stage.
i do it to most cheap powertools here, (someone bought like 10 of those, my guess low$$ was the key) unlike respectable brands, they have simplest charger, with no shut off, so you got to time the charge. but who ever does that?? lol,
especially 18v skill drill batteries suffer from this problem.
i removed flash circuit from disposable camera, soldered 2 wires with nails to capacitor, and zap each cell 2-3- times. it does the trick


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## Battery Guy (Jun 1, 2010)

Ray_of_Light said:


> I mean, during the charge of Ni-CDs, the activation of cadmium surface progresses from the areas already activated; in partial cycling, it is always the same area which participates to the active reactions, while the non-used area becomes non-responding and creates a voltage depression.
> This behaviour is typical of the cadmium, it doesn't happen with the hydrogen-storing alloy of Ni-MH batteries.



I totally get what you are saying here. Essentially, the hypothesis is that during shallow cycling, only a portion of the cadmium electrode goes through oxidation and reduction, and this portion gets physically separated and isolated from the remaining part of the electrode. Only through a slow, deep cycle charge/discharge event is the whole electrode "reformed"

I get what you are saying because this was exactly my thinking 6 years ago. That is, until I mentioned this to a colleague that was doing crystallographic studies on NiOOH. This person told me that I needed to do some more reading on the subject, then mentioned that the voltage depression/memory effect was observed in all battery systems using NiOOH, not just Ni-Cd.

So I did a literature search and a fair amount of reading. Everything I found in the literature agreed on one thing: the memory effect is caused by the NiOOH electrode. There are various interpretations and mechanisms, Huggin's work being the most recent and definitive in my opinion, but I was not able to find anything that points to the cadmium electrode as the cause (except for that Energizer data sheet).

I did more digging today, and still came up empty handed. Not that this proves anything. I still have a few more sources that I am trying to dig into. When I search "cadmium AND battery AND memory" into the ISI Web of Knowledge database, I come up with the following pertinent references with abstracts:

_*Possible cause of the memory effect observed in nickel-cadmium secondary batteries*_

_Author(s): Sato Y, Ito K, Arakawa T, Kobayakawa K
Source: JOURNAL OF THE ELECTROCHEMICAL SOCIETY Volume: 143 Issue: 10 Pages: L225-L228 Published: OCT 1996 

Abstract: After repeated shallow discharging and overcharging of nickel or cadmium capacity-limited cells, a working voltage lowering of the discharge curve was observed. The magnitude of the lowering was higher in the nickel capacity-limited cells. The x-ray diffraction pattern of the charged-state normal nickel electrode contained diffraction peaks due only to beta-NiOOH. A charged-state nickel electrode showing a lowered discharge voltage had diffraction peaks due to gamma-NiOOH, in addition to those due to beta-NiOOH. This may be a cause of the memory effect observed in practical nickel-cadmium batteries._

*The 'memory effect' on nickel oxide electrodes: electrochemical and mechanical aspects*

_Author(s): Davolio G, Soragni E
Source: JOURNAL OF APPLIED ELECTROCHEMISTRY Volume: 28 Issue: 12 Pages: 1313-1319 Published: DEC 1998 

Abstract: Full discharge of nickel-cadmium batteries after sustained overcharge or repeated shallow discharge shows a voltage step generally known as the 'memory effect'. Nickel oxide electrode (NOE) gives a relevant contribution to the memory phenomenon, which has been related to the presence of the gamma-phase. This phase, in fact, had been found by XRD analysis in a charged NOE showing such an effect. This work deals with the mechanical behaviour of NOEs cycled so as to produce the memory effect. During the cycling of asymmetric electrodes, a beading moment occurs during discharge: this is caused by the expansion of the active mass. The force, normal to the plane of the electrode, which equilibrates with the bending moment can be measured, thus giving an indication of the stresses suffered by the sintered supporting structure. Significant differences in both the electrochemical and mechanical behaviour after sustained overcharge and after shallow discharge have been observed. The different behaviours can be related to the unlike distribution of the gamma-phase in the body of the electrode. It is suggested that the shallow cycling produces an accumulation of gamma-phase at the contact with the current collector, whereas during sustained overcharge all the active mass is changed into gamma-phase._

_*Cause of the memory effect observed in alkaline secondary batteries using nickel electrode*_

A_uthor(s): Sato Y, Takeuchi S, Magaino S, Kobayakawa K
Source: BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN Volume: 73 Issue: 8 Pages: 1699-1713 Published: AUG 2000 

Abstract: By repeating shallow discharging and overcharging of alkaline secondary batteries using nickel electrode, a lowering of working voltage is observed on the discharge curve, which is called a memory effect. The X-ray diffraction pattern of the charged-state of the normal nickel electrode contained only diffraction peaks due to beta-NiOOH. A charged-state nickel electrode showing lowered discharge voltage had diffraction peaks due to gamma-NiOOH in addition to those due to beta-NiOOH. The formation of gamma-NiOOH can be attributed to be the main cause for the memory effect commonly observed in alkaline secondary batteries such as nickel cadmium and nickel hydrogen batteries. By XRD analysis and AC impedance study, gamma-NiOOH was found to be initially formed at the current collector side; it grows to the solution side in the course of shallow discharge-charge cycling. Therefore, if the amount of gamma-NiOOH formed is small, only beta-NiOOH can be detected, even when the memory effect is observed. In this case, gamma-NiOOH can be detected by shaving the surface of the electrode using a piece of emery paper to remove covering beta-NiOOH. This gamma-NiOOH disappears within a few cycles of the normal charge-discharge cycling, resulting in the elimination of the memory effect. It may be concluded that the cause of the memory effect is mainly due to the formation of gamma-NiOOH._

_*Cause of memory effect observed in alkaline secondary batteries - AC impedance analysis*_
_ 
Author(s): Takeuchi S, Magaino S, Kobayakawa K, Sato Y
Source: ELECTROCHEMISTRY Volume: 68 Issue: 12 Pages: 977-983 Published: DEC 2000 

Abstract: The cause of the memory effect observed in alkaline-type rechargeable batteries was studied. It is found that gamma -NiOOH initially forms at the collector side and it grows to the solution side as shallow charge-discharge cycling progresses. The charge transfer resistance of the charged-state Ni-electrode increases with shallow charge-discharge cycling. These results suggest that the memory effect is mainly caused by the formation of gamma -NiOOH.
_
_*Cause of the memory effect observed in alkaline secondary batteries using nickel electrode*_

_Author(s): Sato Y, Takeuchi S, Kobayakawa K
Source: JOURNAL OF POWER SOURCES Volume: 93 Issue: 1-2 Pages: 20-24 Published: FEB 1 2001 

Abstract: The cause of the memory effect observed in alkaline-type rechargeable batteries such as nickel-cadmium and nickel-hydrogen batteries was studied using a positive capacity-limited nickel-cadmium cell and AAA-type commercially available nickel-cadmium and nickel-hydrogen batteries. From the X-ray diffraction (XRD) analysis, gamma -NiOOH was observed on the nickel electrode in a charged state after repeating shallow discharge cycling of the cells or overcharging. This gamma -NiOOH is initially formed at the collector side of the electrode and it then grows to the solution side during shallow discharge cycling. When the amount of gamma -NiOOH formed is small, only beta -NiOOH can be detected by conventional XRD, even when the memory effect is observed. In this case, gamma -NiOOH can be detected by shaving the surface of the electrode, using an emery paper to remove the beta -NiOOH covering. This gamma -NiOOH disappeared within a few cycles of the normal charge-discharge cycling and the memory effect disappeared. It is concluded that the cause of the memory effect is mainly due to the formation of gamma -NiOOH. 
_



Ray_of_Light said:


> The reference available on these effects are at least a decade old. In a today academic environment, if you state that the memory effect is caused from nickel, you may lose some of your credibility.



Given the plethora of academic work published that points to the nickel electrode, and zero peer reviewed publications (at least that I can find) pointing to the cadmium electrode as the cause of the memory effect, I am not sure why you think that my credibility is in jeopardy. But like I said, I am still digging into this. Perhaps in a Ni-Cd cell there are two mechanisms that can occur simultaneously, making differentiation between the two difficult?

Also, I think that people can have differing opinions based on similar testing and evidence, without either sacrificing credibility. 

I am also happy to be (and frequently am) proven wrong. I would absolutely love to get my hands on some good published work that proposes and tests a cadmium-based mechanism for the memory effect. I would be sending that along with a good hearted  to my former colleague who told me I was crazy to think that cadmium had anything to do with the memory effect 6 years ago.

Cheers,
Battery Guy


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## Ray_of_Light (Jun 1, 2010)

I believe we are annoying the other members with such indeep discussion of the Ni-CD and Ni-MH batteries. I want just to add something. 

When I stated that you may be considered a shallow person by saying the nickel causes memory effect, I didn't mean you're wrong in absolute; I mean that, academically, the current accepted mechanism for explaining the memory effect is the surface behaviour of the cadmium, and you could be considered a voice out of the chorus. As academic knowledge progresses, this may well change. I have my theory about gamma-NiOOH, and a possible parallel cycle; but I have no means or methods -and interests, at this time - to prove it.

Nickel oxydation states, I must say - are still a mistery. I am aware of the papers you mentioned... I am also aware that any real finding in this specific matter is not being published at this stage, since the untold ongoing battle "nickel vs lithium" for the automotive market. 

All I know is that the results of xray diffraction requires interpretation with QED theories (quantum electrodynamics). I also heard of an explanation involving the energy of the vacuum.

I think we need to wait and see.

For this discussion, we may open a new thread at different time. 

Thanks

Anthony


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## Mr Happy (Jun 1, 2010)

I also had wondered if perhaps there are two complementary "memory" effects going on at the same time. The voltage depression effect is very observable in NiMH cells, but many authorities say this is not the original memory effect described in NiCd cells.

If the voltage depression effect is associated with the nickel electrode, then the same effect ought to be observed in NiZn cells too. Since NiZn cells are now readily available to consumers, this is a hypothesis that can be tested by any of us with some suitable experiments.


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## Mr Happy (Jun 1, 2010)

Ray_of_Light said:


> I believe we are annoying the other members with such indeep discussion of the Ni-CD and Ni-MH batteries.


They don't have to read the thread you know. Reading any given thread is entirely optional 

In actual fact, this kind of thread is far more interesting than endless repetitions of the same old questions like "What is the best charger to buy?" and "Do you need to run a break-in cycle on Eneloops before using them?"


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## alpg88 (Jun 1, 2010)

^^agreed.
buttom line is who cares how it happens, it just does, we know how to avoid it, and that is good.
now i'm going to use sub c nicd from dewalt battery to power my 30w6v par 36. can't wait till FM ships me mine par 36 mag head.


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## 45/70 (Jun 1, 2010)

Mr Happy said:


> In actual fact, this kind of thread is far more interesting than endless repetitions of the same old questions like "What is the best charger to buy?" and "Do you need to run a break-in cycle on Eneloops before using them?"



Aww, come on Mr H. What better way to boost up that post count than those favorites? 

Personally I find the discussion interesting, but perhaps a bit more detailed than I need. That doesn't mean others, besides those already involved, aren't wanting to learn more about it.

When questions are asked about whether NiMH cells have a "memory" problem, or NiCd vs. NiMH memory comparisons come up, I refer folks to Buchmann's article on the subject. It seems to cover all the bases well enough, without going into great detail.

Dave


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## Battery Guy (Jun 1, 2010)

Ray_of_Light said:


> When I stated that you may be considered a shallow person by saying the nickel causes memory effect, I didn't mean you're wrong in absolute; I mean that, academically, the current accepted mechanism for explaining the memory effect is the surface behaviour of the cadmium, and you could be considered a voice out of the chorus.



I just don't get where you are coming from here. If the academically accepted mechanism is the cadmium electrode, then where are the peer-reviewed articles supporting this? I posted several references that point to the nickel electrode, and I really only scratched the surface. I really tried to do an exhaustive search, but came up empty on the whole cadmium electrode thing. 

I think the Buchmann article that 45/70 linked to is interesting. This article indicates that in a Ni-Cd cell, more than one mechanism contributes to the memory effect, and that in other systems with nickel positive electrodes, only one mechanism is present. I am happy to leave it at that.

Cheers,
Battery Guy


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## Chauncey Gardner (Jun 1, 2010)

Ray_of_Light said:


> I believe we are annoying the other members with such indeep discussion of the Ni-CD and Ni-MH batteries. I want just to add something.
> 
> When I stated that you may be considered a shallow person by saying the nickel causes memory effect, I didn't mean you're wrong in absolute; I mean that, academically, the current accepted mechanism for explaining the memory effect is the surface behaviour of the cadmium, and you could be considered a voice out of the chorus. As academic knowledge progresses, this may well change. I have my theory about gamma-NiOOH, and a possible parallel cycle; but I have no means or methods -and interests, at this time - to prove it.
> 
> ...


 
I really enjoyed reading this thread. It started out with some guys bitching about thier cordless tools battery life & wound up becoming a mini tutorial for those interested enough to read.

This came off as bit dismissive & insulting to me (directed at Battery Guy) & a patronizing way to say, "_time to end the thread now."_
It wasn't the first personal swipe at him either.

Just .05 from an interested reader (_who's more convinced he finally got the right cordless tools) _who got something out of the discussion.

Thanks for all of the information, it was interesting.


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## TorchBoy (Jun 1, 2010)

*Re: Why did power tools skip over NiMH batteries?*



Ray_of_Light said:


> I also heard of an explanation involving the energy of the vacuum.


I've got to hear this one.


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## Ray_of_Light (Jun 1, 2010)

Chauncey Gardner said:


> IThis came off as bit dismissive & insulting to me (directed at Battery Guy) & a patronizing way to say, "_time to end the thread now."_
> It wasn't the first personal swipe at him either.



I apologise. I was genuinely worried about bothering other members with theoretical explanations - while the thread meant to talk of something related to this, but different. It wasn't my intention to be dismissive.

To BG. I tend to believe, and this is more a qualified opinion than a scientific certainty, that the mechanisms producing the memory effect in Ni.MH batteries are more than one. I share rhe point of view expressed from Buchmann. Articles, books and electrochemistry university lessons from my school time ( 25 - 30 yrs ago) were invariably mentioning the cadmium as the cause of the memory effect. 
You will not find those lessons and books online, believe me. 

I come to the point now. Try to find an answer to this question: Why, an all descriptive properties of Ni-MH batteries, on every package, on every appliance using them, there is specified in bold letters, "No memory effect" ?
Because on the onset of Ni-MH batteries, early '90, that was the mainstream understanding: no cadmium, no memory effect. I have read countless papers, partecipated to long discussions, and this belief was unanimous. I don't know why these papers haven't been ported to the Net: at the time there were none, so is today. 
But the beliefs has stayed. Knowledge has progressed in the meantime, and the new researches have seen the light (some of them) on the Net. Therefore, you find a majority of pro-nickel and no pro-cadmium. But in the schools (and paper textbooks) the old indications are still deeply rooted.
I dont' know your age and experience, but believe me on the fact that the core of knowledge regarding batteries is not published on the Net. 
It is my opinion that bleeding edge researches in the scientific sector is not anymore the solid-state physics... but batteries. Yes, batteries. 

When I find myself in this type of impasse, my reaction is to experiment. It is relatively easy to establish if memory effect is present in Ni-MH, and make a comparison with Ni-CD. The answer is under everybody' eyes. To overcome the memory effect of Ni-MH we all do... break-in cycles. But... do we measure voltage increase after break-in cycle in Ni-MH, like we measure in Ni-Cd?
No, it isn't 100 mV increase.
Therefore, there are two memory effects. In one of my previous posts in this thread, I briefly mentioned that the memory effect of the nickel is often confused with that of the cadmium; it wasn't my intention to go in this deep explanation.
All in all, the mentioned article from Buchmann is the most correct paper I've seen on Internet.

Now, to Torchboy.
Vacuum energy is the energy that is contained in the free space even when there is no mass or radiations; it has never been observed, but it has been deduced from various effects and measurements: the spontaneous emission of photons from materials, Van der Waals forces, the difference of energy of the S and P orbitals of the hydrogen atom, and many others. 
In accordance with the quantum scientists, the empty space is not empty, but all the interactions happening in the vacuum cancels out, almost entirely. The “almost” shows up as a tiny attraction of metal objects in space due to resonance, which has been verified experimentally.
This attraction, due to the vacuum energy, seems to have a role in the beta and gamma -NiOOH interactions. 
I dont' know more.

Time for bed

Regards

Anthony


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## 45/70 (Jun 1, 2010)

Ray, I can see it now. The next generation of batteries. "Vacuum cells"! Cylindrical cells with a zero atmosphere contained within containing, well.... nothing! Think of the weight savings these cells will provide!

Dave


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## VegasF6 (Jun 1, 2010)

Still ticking:


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## HarryN (Jun 2, 2010)

Well, I am enjoying the depth of the thread, even though I don't entirely agree with some of the publications. 

What I do agree with, is that Ni based cells might end up giving Li a run for its money in some applications that everyone assume will go Li, if for no other reason than availability.


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## bulbman (Jun 3, 2010)

Nimh power tools? Try leaving an nimh cell in the garage in winter


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## Richwouldnt (Apr 19, 2011)

bulbman said:


> Nimh power tools? Try leaving an nimh cell in the garage in winter


 
Or in a contractor's truck that is parked overnight outside. Iwas not really aware of the temperature consideration with NIMH cells.

Thanks for a very interesting and informative thread I thought worth reviving. My portable phone experience is that the NIMH AAA cells in my current Panasonic wireless phones far outlast the Nicad packs in the older ones I used to use. Also they are replaceable with off the shelf NIMH cells rather than being a special proprietary battery pack. Longer life and much greater capacity but in a low current drain situation compared to power tools though.

I am considering trying to rebuild some 12v and 18V Ryobi Nicad battery packs which finllly died. I still need to open them up and determine cell size used.


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## fyrstormer (Apr 20, 2011)

TakeTheActive said:


> If you're going to use a power drill once or twice a year, you CERTAINLY don't need a cordless one! DAILY, or at least a few times a week, maybe...


You, sir, have never built something in the woods. Mountain bikers usually have to fix their own trail reinforcements, and while it may only be necessary to fix something once a year, it's definitely not practical to carry several miles of extension cord.


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## fyrstormer (Apr 20, 2011)

alpg88 said:


> that is exactly what i had when i bought my old appt. crown moldings installed with Sheetrock screws, plus the fact that concept of leveled lines were not known to them. whoever did that should really not do any home improvements ever again. i spend 3 days ripping them off, spackle, and mount new moldings the right way, with a level, and a nail gun.


Leveling your woodwork is always a good idea, but I'm not a big fan of nails. They're easy to install, but they always pull loose eventually. I'd rather use screws even if it means I have to be more careful.


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## fyrstormer (Apr 20, 2011)

BatteryCharger said:


> Oh, you HAD to go and say it! I've already got seven drills...that doesn't mean I don't need more. (right?) :duh2:


Mwahahaha, hahaha!


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## fyrstormer (Apr 20, 2011)

Ray_of_Light said:


> Crystallographic studies conducted with X-ray mulecular diffraction are clarifying the previously unknown behavior of yada yada yada


I only partially comprehend this post, but my brain is tingling anyway.


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## Bullzeyebill (Apr 21, 2011)

Responding to this old thread is a waste of time, and not very productive.

Bill


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