# How far can LiIon be discharged?



## HKJ (Apr 6, 2016)

[size=+3]How far can LiIon be discharged?[/size]







I do often see a question about how far LiIon can be discharged and if it is safe to charge a discharged LiIon. These questions can be fairly difficult to answer precisely, LiIon manufactures do not publish much about it and LiIon is not just LiIon, there are many different chemistries with similar but not equal specifications.



[size=+2]How to measure the discharge cut-off voltage?[/size]

Some people do not wish to discharge below 3.6 volt (or something), but why stop there when the specifications say 3.0 or lower?
There is some sort of reason for this and it has to do with how you measure voltage: Usual voltage is measured with the battery out of the equipment, i.e. the battery is unloaded. Here is an example:






Here I discharge a cell to 2.5 volt with 2A, when I stop the voltage jumps to 3.3 volt and it jumps fairly fast.






Zooming in on the stop, the curve shows 3 minutes. It takes 12 seconds for the voltage to raise from 2.5 volt to 3.1 volt. This means that if you take the battery out and measures it you will never see the 2.5 volt.






Lets try with another cell.






This is also a 3 minute view, the voltage raises from 2.5 volt to 3.1 volt in 3 seconds and in 7 seconds it is about 3.2 volt. Again it is not possible to measure the voltage where the equipment turns off.

How far the voltage jumps depends on the discharge current, a lower current will give a smaller jump and on the battery chemistry, different chemistries gives different voltage jumps. This means that measuring voltage with the battery out of the equipment will not give a correct indication of the minimum voltage the equipment discharged the battery to.

Due to the above jump in voltage it is rather difficult to know what the actual battery voltage is inside the flashlight when it is on and the safe way is to assume it is empty when the unloaded voltage is below some value. The 3.6 volt is fine for some batteries, but it is possible to go lower with many modern cells as seen above. The table at the end of the remaning capacity article can also be used.



[size=+2]How far to discharge batteries during normal use?[/size]

The first answer to this is easy, check the datasheet:






Here are some values from 4 different datasheets. The most common values are 2.75V and 2.5V today.

These values are the lowest voltage that is allowed on the battery if the full lifetime must be reached*. This means that for any normal usage this is the lowest value to discharge the battery to. This voltage do not include any current, i.e. the limit is *not* one that can only be discharged to at high currents, it is allowed to discharge with a very low current to this specification.
It is not within specifications to discharge below this voltage, just because the battery will recover to above this voltage when the load is removed.

*Usual, the 2.0 volt specification is not used for lifetime tests on that cell, there the lower limit is 2.5 volt.


[size=+2]But my over-discharge protection do first trip at 2.3 volt, is it faulty?[/size]

Usual no, protection is normally not used, i.e. it is allowed to go outside the range for best lifetime.






Here is some data from Samsung, the over-discharge protection is supposed to be outside the normal usage range.






And if I include a bit more of the table it can be seen that it varies with application. At high current the protection can be at a lower voltage.
From this table it looks like it is acceptable to discharge LCO/LMO (Real ICR/IMR) cells below minimum value, when it is done at high current, but with the more modern cells it is best not discharging too much below rated voltage.



[size=+2]How low voltage is safe to recharge?[/size]

Here are some illustrations from LiIon handbooks:











In both illustrations there is:
Operating range, that is the voltage range from the datasheet.
Protection/safety range, that covers a wider voltage range, but may add extra wear to the battery.
Keep out/unusable range, that is very low or very high voltage and the battery is dangerous.






The Samsung guidelines also list a minimum voltage.

These 3 items gives the minimum voltage as 1.5 volt, somewhere below 2.3 volt and 1 volt. This covers different brands and different chemistries.
Another importance detail is pre-charging, when the voltage is low the battery must not be charged at full current. A reduced current must be used.
When a battery is discharged to this low voltage it may lose some capacity and will lose some lifetime.

The reason to not charge very discharged batteries is because the chemistry breaks down at low voltages, depending on how much the chemistry has degraded the battery may explode when charged!



[size=+3]Conclusion[/size]

With the above as basis I will recommend the following:
1) Do not use over discharge protection as signal for when to charge batteries, it might wear the batteries down faster.
2) Do not charge batteries measuring below 2 volt, except if you have data saying it is safe.
3) When cells are down to 3.3 to 3.6 volt unloaded they are empty according to my tests, when the load is a few ampere.
4) Just because the cell recovers voltage, do not make it advisable to discharge below the limits while current is on.

And remember that if a battery gets hotter than usual during charger and/or will not charge fully (i.e. charger will not terminate), it is dead and maybe dangerous.



[size=+3]Notes[/size]

This article uses excerpts from:
Lithium Ion Rechargeable Batteries Technical Handbook (Sony)
Lithium Ion Batteries Technical Handbook (Panasonic)
Pack Design Guideline (Samsung datasheet, I have done some cut and paste in the table)

More voltage jumps with and without load


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## ven (Apr 6, 2016)

Thanks for the info, very interesting!

Lowest i tend to go down to is 3.3v on my ecig mods, flashlights tend to be around the 3.6v-3.8v on average. Usually end up topping them off after set times for convenience and knowing i will be using again soon(work lights for example).


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## Capolini (Apr 6, 2016)

Thanks for the nice info.



EDIT: My cells are between 3.6v and 3.9v after use. A good thing about using 2 or 3 lights a night for my hikes w/ *CAPO* is that One light is never used more than 30 minutes so the batteries never get drained too much!

15 minutes of use w/ my M2Xvn gives a voltage of 3.89v W/ a *18650 LG HG2 IMR 3000mAh. :thumbsup: *I always have 2 w/ me.A fresh one after 15 minutes!*

*30 minutes of use w/ 4 X 18650 K'power 3400mAh w/ my TK61vn V4 yields a voltage of 3.78v!*
*


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## Gauss163 (Apr 6, 2016)

Good choice of topic. It would help to explain a bit about the reason for the voltage drop / bounce, i.e. say something about internal resistance, maybe even mention some simple cell models using resistor(s) and capacitor(s) (the motivation being that it is better to teach them how to fish than to serve them fish on a platter, i.e the better _conceptual _model that the reader has, the easier they can answer such FAQs on their own).


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## KeepingItLight (Apr 6, 2016)

Thanks, HKJ!

The technical information you publish is some of the best CPF has to offer.


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## HKJ (Apr 6, 2016)

Gauss163 said:


> It would help to explain a bit about the reason for the voltage bounce, i.e. say something about internal resistance, maybe even mention a simple equivalent cell model using a resistor and capacitor



The idea of a equivalent circuit is not very good, the resistor changes significantly when the cell is near empty. In the linked article I discharge a cell in 100mAh steps, there it is easy to see.


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## lightlover (Apr 6, 2016)

KeepingItLight said:


> Thanks, HKJ! The technical information you publish is some of the best CPF has to offer.



+1 
HKJ is a Bright Star 
(Even if I have to study his posts, and still only "get" only about 50% of the content ...)


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## MAD777 (Apr 6, 2016)

Can't say enough how valuable all your input is to the forum, HKJ! Fantastic post!

This should be a permanent stickie or tutorial. Definitely required reading material.


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## archimedes (Apr 6, 2016)

A lot of this information is difficult to find.

Thank you very much for all of your educational contributions here, and your extensive and ongoing testing [emoji106]


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## ven (Apr 6, 2016)

Agree HKJ is awesome!!!:rock::bow:


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## Gauss163 (Apr 6, 2016)

HKJ said:


> The idea of a equivalent circuit is not very good, the resistor changes significantly when the cell is near empty. In the linked article I discharge a cell in 100mAh steps, there it is easy to see.



There are many different equivalent models used for pedagogical purposes - some more complex than others. For the purpose at hand, that simple model suffices. Most textbooks on batteries present a variety of such.

For a simple example from a study in 2015 see this later post.


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## Gauss163 (Apr 6, 2016)

Below is a brief exposition on voltage drop/bounce, excerpted from a paper by one of TI's battery gurus: Battery Selection, Safety, and Monitoring in Mobile Applications, by Yevgen Barsukov, Texas Instruments. See also this later post which includes graphs from a recent study illustrating how highly accurate such simple models my be. Readers interested in more precise battery models can find them in most textbooks on batteries.


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## sidecross (Apr 6, 2016)

Thank you HKJ for this information.

From my own personal use I try to use my single cell batteries down to 3.5 volts under load by trying to check voltage after certain time and load usage. To do this I keep one or two extra batteries in easy reach so I can check voltage at a later time.

After an amount of usage I begin to see a trend of how load and time effect my own battery usage.

With the method I use I discard batteries that do not charge back to at least 4.19 to 4.18 volts. Battery prices for quality 18650 flat top batteries are found at a reasonable price, so the expense for replacement is within my budget.

There is much to learn about lithium ion batteries and every user should be making an effort to increase their understanding.


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## HorizontalHunter (Apr 6, 2016)

Very nice explanation of a complex topic. 

I always enjoy reading your posts and reviews. They are always informative and educational.

Thank you,

Bob


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## KITROBASKIN (Apr 6, 2016)

The NiteCore TM36 and others are able to show voltage under load, though it is with multiple cells. 

Interesting and relevant post. A Big Thank You.


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## HKJ (Apr 7, 2016)

Gauss163 said:


> There are many different equivalent models used for pedagogical purposes - some more complex than others. For the purpose at hand, that simple model suffices. Most textbooks on batteries present a variety of such.



As you have already shown with you post of a model circuit it is not that simple and it do not really represent the situation at the end of discharge (As this article is about).


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## shk (Apr 7, 2016)

Great information, very helpful! Never know that voltage will bounce back. Thank you HKJ!


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## SG Hall (Apr 7, 2016)

Thanks HKJ, great information that's practical.


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## Gauss163 (Apr 7, 2016)

HKJ said:


> As you have already shown with you post of a model circuit it is not that simple and it do not really represent the situation at the end of discharge (As this article is about).



It is about as simple as one can get. If you think that there is a simpler way to teach these basic ideas then let's see it. 

Why do you believe that "it do not really represent the situation at the end of discharge"? Please be more precise.


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## HKJ (Apr 7, 2016)

Gauss163 said:


> It is about as simple as one can get. If you think that there is a simpler way to teach these basic ideas then let's see it.
> 
> Why do you believe that "it do not really represent the situation at the end of discharge"? Please be more precise.



This article is not about how batteries reacts to fast load pulses and that model is valid from 1Hz to 1MHz (If you have the correct values to fill in). There is nothing in that model to handle the behaviour of the rising Ri when the battery is near empty. I do cover basics in batteries without complex schematics with a lot of unknown component values.


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## akhyar (Apr 7, 2016)

Thumbs up again for excellent write-up HKJ.
Very informative


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## Gauss163 (Apr 7, 2016)

HKJ said:


> This article is not about how batteries reacts to fast load pulses and that model is valid from 1Hz to 1MHz (If you have the correct values to fill in). There is nothing in that model to handle the behaviour of the rising Ri when the battery is near empty. I do cover basics in batteries without complex schematics with a lot of unknown component values.



It seems you may be missing the point. As I said above, the goal was to provide a simple explanation of the role that internal resistance plays in voltage dropping / bouncing. Lack of knowledge about this is at the heart of many FAQs here (including the matters you address above). 

More precise models are not required for such basic _qualitative _understanding of the underlying phenomena.


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## HKJ (Apr 7, 2016)

Gauss163 said:


> It seems you may be missing the point. As I said above, the goal was to provide a simple explanation of the role that internal resistance plays in voltage dropping / bouncing. Lack of knowledge about this is at the heart of many FAQs here (including the matters you address above).
> 
> More precise models are not required for such basic _qualitative _understanding of the underlying phenomena.



If that is the goal, then write an article about it. Again: This article is about when batteries run empty. The voltage recovery in this case is more than twice the value compare to a battery with some energy left and if it happens instantaneous or over some time do not really matter (The model your published covers neither case).

The interesting part is that there is a significant voltage recovery, it is fast enough to prevent measure the discharge end voltage and it varies with a couple of factors. I believe I have covered all of that.


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## psychbeat (Apr 7, 2016)

Great write up HKJ - thank you. 

In my experience it is VERY noticeable when a cell is close to empty -i.e. The light gets dimmer or steps down. 
Even with my direct driven lights being left on Ive rarely had a cell go below 3v unloaded/resting. 

I much prefer the dimming or stepdown on bare/unprotected cells than th cutoff of a protection circuit. 

Seems like even in a direct driven led scenario it's hard to drain a modern cell to dangerous levels due to the VF of the emitter and rising IR of the cell.


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## Gauss163 (Apr 7, 2016)

HKJ said:


> If that is the goal, then write an article about it.



See above - I already posted a short exposition by an expert in the field.



HKJ said:


> Again: This article is about when batteries run empty. The voltage recovery in this case is more than twice the value compare to a battery with some energy left and if it happens instantaneous or over some time do not really matter



For _qualitative _understanding it matters little that the bounce is bigger at the end of discharge. What matters is that it is significant and prevents said naive measurements from succeeding. The same holds true for the termination of any (dis)charge at any point, or, more generally, for any nontrivial change in current (for nontrivial time). But this will not be clear from what little is said in the OP.



HKJ said:


> (The model your published covers neither case).



The models convey accurate _qualitative _understanding of the reason for the voltage bounce. Precise _quantitative_ understanding is not required for the above purposes (nor is it conveyed _generally _by the single graph in the OP).



HKJ said:


> The interesting part is that there is a significant voltage recovery, it is fast enough to prevent measure the discharge end voltage and it varies with a couple of factors.



Yes, but simply pointing at a graph and saying "this is what happens" is not the same as imparting some conceptual understanding of the underlying phenomena. Unlike a graph, models apply generally and allow one to make very general inferences. For example, from what little is said in the OP it will not be clear that, by symmetry, a voltage drop occurs at the end of a charge, and that these bounces are (roughly) proportional to the current, and that analogous bounces occur with any nontrivial change in current. These and related inferences are all immediate if one understands any basic model incorporating internal resistance (which requires only basic knowledge, viz. Ohm's law). 

Of course one needs more complex models to deduce more precise _quantitative _information - which requires understanding how internal resistance depends on various parameters (SOC, temperature, etc), and the role played by time constants of various internal processes, etc. But none of this complexity is required in the OP.


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## psychbeat (Apr 7, 2016)

^^^


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## sidecross (Apr 7, 2016)

Arguing the exact count of 'how many angels can dance on the head of a pin' is in the next room down the hall. :wave:


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## scintillator (Apr 7, 2016)

Thank you for the great post HKJ.


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## SubLGT (Apr 7, 2016)

Gauss163 said:


> Below is a brief exposition on voltage drop/bounce, excerpted from a paper by one of TI's battery gurus….



I only understood about 15% of this "brief exposition". I understood 100% of the original post.


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## MAD777 (Apr 7, 2016)

SubLGT said:


> I only understood about 15% of this "brief exposition". I understood 100% of the original post.


My thoughts exactly! 👍


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## Gauss163 (Apr 7, 2016)

SubLGT said:


> I only understood about 15% of this "brief exposition". I understood 100% of the original post.



It goes without saying that diving deeper into the underlying science requires further effort. But you only need to understand a small part of that article to grok the role played by internal resistance. Once you do, you'll have a much deeper understanding of the essence of the matter.


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## Milw light (Apr 7, 2016)

Thanks HKJ, you the best.


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## seery (Apr 7, 2016)

Thanks HKJ!


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## KeepingItLight (Apr 8, 2016)

I, for one, appreciate the extra detail. I copied out the section Gauss123 posted from a battery textbook. That's okay for me. As it turns out, I am minimally qualified to understand it! It is right at the boundary of my existing knowledge, so I learned something. 

What bothers me, however, is the tone that these discussions sometimes take on. When they become contentious, they are uncomfortable to read.


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## HarleyXJGuy (Apr 8, 2016)

lightlover said:


> +1
> HKJ is a Bright Star
> (Even if I have to study his posts, and still only "get" only about 50% of the content ...)



I agree but if you are able to understand 50% of this material my hat is off to you. Still that said I learn more everytime I come here.


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## HKJ (Apr 8, 2016)

HarleyXJGuy said:


> I agree but if you are able to understand 50% of this material my hat is off to you. Still that said I learn more everytime I come here.



It is possible to ask questions to my articles and reviews and there are usual some that answers (either me or other).


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## ven (Apr 8, 2016)

HarleyXJGuy said:


> I agree but if you are able to understand 50% of this material my hat is off to you. Still that said I learn more everytime I come here.




There is always something to learn, i know for a fact what i know today(not much) will be not as much as tomorrow............thanks to many members and certainly a mr HKJ. 

What seems complex over time falls bit by bit into place.............No need to get anal with stuff(unless you want to of course), enough to understand the basics and a bit more.........Cells and chargers are a whole new world, made interesting by HKJ and the time he takes in his threads. 

Then just ask, no such thing as a stupid question as long as you dont mind stupid answers :laughing: 

Not sure just fire away!!!


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## sidecross (Apr 8, 2016)

KeepingItLight said:


> I, for one, appreciate the extra detail. I copied out the section Gauss123 posted from a battery textbook. That's okay for me. As it turns out, I am minimally qualified to understand it! It is right at the boundary of my existing knowledge, so I learned something.
> 
> What bothers me, however, is the tone that these discussions sometimes take on. When they become contentious, they are uncomfortable to read.


+1

I agree about it being 'uncomfortable to read', but from my reading of science history the arguing about who is most correct is a characteristic that is often found.


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## recDNA (Apr 8, 2016)

Great work! I usually charge at 3.7 volts but have occasionally charged batteries at 3 volts and a couple that protection had tripped with no reading at all. Now I kind of think I should recycle them because they may have been very low under load. I never knew that.


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## degarb (Apr 8, 2016)

Excellent info. I must save it. Read it slower next time.

My Panas.3400s from fasttech cut off at 2.5, while the kiadomain cutoff at 3.0 volts. I know the capacity, and use only cc 700ma driver. I am guilty of relying on the runtime and protection in cells for recharge indication. I do try to keep a volt meter near charger, since overcharging is reason for explosion. But need to invest in a one handed voltage check. Though a charger should have a button to press to display voltage. I am dreaming, probably.


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## degarb (Apr 8, 2016)

"but have occasionally charged batteries at 3 volts and a couple that protection had tripped with no reading at all. Now I kind of think I should recycle them because they may have been very low under load."

My understanding is that if the protection trips in, you should read 0 volts. You must briefly "jump start" the cell to reset the protection circuit, much as you jump start a car battery. Then you won't get the bad battery blink from your charger. Only my Fenix charger would charge a tripped cell without first jumping it. 

After all, that protection circuit isn't just overcharge protection (to avoid explosion), but undercharge protection (to avoid hurting the cell). And, I guess, short circuit protection too (to avoid overheating and exploding cell).

On youtube, it is fun to spend an hour watching cells explode by putting them on the stove, or overcharging them.


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## HarleyXJGuy (Apr 8, 2016)

HKJ said:


> It is possible to ask questions to my articles and reviews and there are usual some that answers (either me or other).



Oh yes, I have found people here to be very helpful.

Using your DMM article I went out and got one to test my batteries with. Noticed pulling them off the charger they would read 4.2V. After ten minutes or so I checked them expecting a little drop off in voltage but found none. Still 4.2. Is my memory faulty or did I read somewhere there would be a slight drop after some time the charger? These a new cells if that matters.


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## HKJ (Apr 8, 2016)

HarleyXJGuy said:


> Oh yes, I have found people here to be very helpful.
> 
> Using your DMM article I went out and got one to test my batteries with. Noticed pulling them off the charger they would read 4.2V. After ten minutes or so I checked them expecting a little drop off in voltage but found none. Still 4.2. Is my memory faulty or did I read somewhere there would be a slight drop after some time the charger? These a new cells if that matters.



Your charger will probably be charging a little bit above 4.2 volt. The voltage drops most in the first few minutes and the drop is very depends on the cell age and the charges termination current.
You can see a bit more here: http://lygte-info.dk/info/BatteryCharge4.2V UK.html


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## novice (Apr 9, 2016)

I appreciate the information presented here, and have bookmarked it. I need to ask a question at a pre-school level, since even though I am a longtime member, I am electronics-challenged.

Several of the members on the first page of this thread state that they will allow their batteries to drop down to 3.5 volts, or 3.6 volts. HKJ has noted how taking a Li-ion out of a flashlight will allow the voltage to "bounce back up" after only 12 seconds, i.e., faster that it is possible to get a DMM on those cells.

My question is, if I take AW Li-ion cells (either protected or IMR) out of a flashlight (and assuming 12 seconds pass), _what are the lowest voltage levels I should be allowing for that cell _(that is now at rest) to provide for maximum cell longevity? Is it possible to answer that question without bringing mAh factor into it (I'm not being rhetorical)? Perhaps this thread has already answered this question, but I didn't understand. Thank you!


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## ven (Apr 9, 2016)

Will try and use some of my working voltages for examples

I just use a basic figure, 3.3v on some of my mods, around 3.6-3.8v on my lights before topping off............

The reason i dont take lights down to that is loss of higher modes(light dependent/output level)and my uses dont really take me that low anyway..........

Now my 25R or LG cells i use in my mods, i tend to ask around 9a on average, 2 of my mods will work down to 3.3/3.4v(depending on cell and age) before stepping in with 20% or less(thats what i have set one to). So even at 3.5v, it can supply 9a bursts for 5-8 seconds(about my vape/draw time). When the sag gets bellow a set V , it warns me and i simply charge the cell up. With my kangertech platinum, when i place the cell on charge, it always reads around 3.3/3.4v again cell dependent as all will have different resistance built up.

I would say the lowest would be 3v, no lower or you will shorten the cycle life, ideally 3.3v or more i would want to see(thats me, HKJ is far more experienced as with others)


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## Gauss163 (Apr 9, 2016)

novice said:


> My question is, if I take AW Li-ion cells (either protected or IMR) out of a flashlight (and assuming 12 seconds pass), _what are the lowest voltage levels I should be allowing for that cell _(that is now at rest) to provide for maximum cell longevity? Is it possible to answer that question without bringing mAh factor into it



Despite incorrect remarks to the contrary in the OP, to assess degradation due to overdischarge what matters most is not how low the _voltage _drops under load but, rather, how low the _capacity _drops. 

As you probably know, the capacity is a function of the _open-circuit (resting)_ voltage of the cell. So, for example, if after use the resting voltage is over 3V then the cell was drained to less than 100% depth, so little if any degradation will have occurred (even if the voltage dropped much lower _under load_). Note that you may need to wait at least 15 minutes or more after removing the load for the cell to attain a relatively stable resting voltage, esp. for older cells with high IR.


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## sidecross (Apr 9, 2016)

Response to novice:

The advantage of a rechargeable lithium ion battery is its being able to be reused a good number of times. To reach the greatest potential of this characteristic is to learn the limits of the battery's discharge. 

In doing this I use a surplus of extra batteries and a notebook to document my use. With what was a short learning curve, I began to see a paradigm of usage to voltage drop. I would tend to first error on the conservative side to gain my data.


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## novice (Apr 9, 2016)

Gauss163 and sidecross, thank you. To forge ahead in my inimically obtuse way; is 3.0 volts (and above) a fairly good "universal" voltage reading to aim for after allowing the Li-ion cells to rest for 15 minutes, after use?


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## sidecross (Apr 9, 2016)

novice said:


> Gauss163 and sidecross, thank you. To forge ahead in my inimically obtuse way; is 3.0 volts (and above) a fairly good "universal" voltage reading to aim for after allowing the Li-ion cells to rest for 15 minutes, after use?


I am for 3.5 volts, but this is my own preference. I try to obtain the most efficient and least wasteful use of lithium ion batteries.

I check my battery voltage when I come back to my home; in the field depending on my use, I have newly charged batteries.


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## Gauss163 (Apr 9, 2016)

novice said:


> Gauss163 and sidecross, thank you. To forge ahead in my inimically obtuse way; is 3.0 volts (and above) a fairly good "universal" voltage reading to aim for after allowing the Li-ion cells to rest for 15 minutes, after use?



You will probably find that most users prefer not to push to the limit but instead choose more conservative values in the range 3.3-3.5V in order to increase the chances of prolonging cell life. But it is helpful to know the limits. Occasionally even conservative users may desire to push closer to the limit in exceptional circumstances where more capacity is needed.


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## MAD777 (Apr 9, 2016)

Something to consider when trying to predict how low the voltage under load really was, is how much current was in play. 

If I understood correctly, a flashlight used on moonlight mode wouldn't have a huge bounce in voltage at the end. 

However, a high powered, 10,000 plus lumen, modded flashlight pulling say 11 amps on turbo, would have a tremendous bounce. This latter scenario would call for a very conservative approach, assuming my understanding is correct.


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## sidecross (Apr 9, 2016)

Gauss163 said:


> You will probably find that most users prefer not to push to the limit but instead choose more conservative values in the range 3.3-3.5V in order to increase the chances of prolonging cell life. But it is helpful to know the limits. Occasionally even conservative users may desire to push closer to the limit in exceptional circumstances where more capacity is needed.


+1

This is too is a good understanding of the battery use.


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## Gauss163 (Apr 9, 2016)

MAD777 said:


> .. However, a high powered, 10,000 plus lumen, modded flashlight pulling say 11 amps on turbo, would have a tremendous bounce. This latter scenario would call for a very conservative approach, assuming my understanding is correct.



It's the opposite: a high current - due to IR voltage sag - reaches termination voltage far before it comes close to 100% DOD (depth of discharge), so it is far from reaching the dangerously low capacity (> 105% DOD) where copper dissolution occurs. But a very low current has tiny IR sag so it won't reach termination voltage till it drains to almost 100% DOD - much closer to the danger zone.

Note that the remarks above pertain only to the effect of _overdischarge _on health, not other aspects. For example, discharging at higher currrent is generally less healthy than at lower currents. To obtain an accurate evaluation of health impact you have to look at the complete picture, taking into account all factors which may impact health, safety, etc.


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## MAD777 (Apr 9, 2016)

Thank you for clearing that up Guass!


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## novice (Apr 10, 2016)

Thank you all so very much for your information!


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## candle lamp (Apr 21, 2016)

It's a quite informative and excellent thread. Thank you so much for your effort and time. HKJ! :thumbsup:

The min. voltage (2.0V) of over-discharging protection for power-tool is much lower than expected.

In my opinion, the flashlights with single cell or more seem to belong to portable IT.

Do you have any plan to test overdischarge of ICR 18650 and compare to non-overdischarged cell in terms of the performance, capacity, etc?
You are one of the busiest man in the world, but I do hope you will do that some day. :bow:


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## HKJ (Apr 21, 2016)

candle lamp said:


> In my opinion, the flashlights with single cell or more seem to belong to portable IT.



It is a question of current draw, a power tool has very high current draw (usual in short pulses), you can find some special flashlights that goes into that category.



candle lamp said:


> Do you have any plan to test overdischarge of ICR 18650 and compare to non-overdischarged cell in terms of the performance, capacity, etc?
> You are one of the busiest man in the world, but I do hope you will do that some day. :bow:



I am thinking about it, it do not need much of my time, but will probably need a month or two on some test equipment. It is definite possible, but I do not have spare equipment at the moment.


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## Gauss163 (Jun 1, 2016)

HKJ said:


> Gauss163 said:
> 
> 
> > It would help to explain a bit about the reason for the voltage bounce, i.e. say something about internal resistance, maybe even mention a simple equivalent cell model using a resistor and capacitor...
> ...



Au contraire, to show just how good even simple equivalent circuit models can be I quote from a study in 2015 that I mentioned yesterday. Notice the very good correspondence between experimental and simulated data for the tested Panasonic 3400mAh cells. I quote from p. A1598:

"An equivalent circuit model for capturing characteristics of Li-ion cells has previously been presented by Andre et al.6,7 This circuit consists of five different regions, namely

- Inductive reactance of metallic elements in wires and cell
- Ohmic resistance of the cell, sum of the resistances of current collectors, active material, electrolyte and separator
- Solid Electrolyte Interface (SEI) resistances
- Electrode charge transfer resistance and double layer capacitance, and
- Diffusion processes within the active material

Using this equivalent circuit, all of the impedance spectra obtained for the cells were modelled. Figure 7 shows a plot of experimental vs. modelled data and the equivalent circuit, and the model output data is presented in Table V. The chi-squared (χ2) minimized to below 10^(−2) in all cases, indicating very good agreement between data and fitted model."


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## space-cowboy (Jun 1, 2016)

HKJ 
Good work like always.

You are choosing very interesting and useful topics .
:twothumbs


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## HKJ (Jun 2, 2016)

Gauss163 said:


> maybe even mention a simple equivalent cell model using a resistor and capacitor...





Gauss163 said:


> Au contraire, to show just how good even simple equivalent circuit models can be I quote from a study in 2015 that I mentioned yesterday.



A simple model with a resistor and capacitor? Then why do you show a model with 4 resistors, 3 capacitors and 1 inductor. Adding enough part and you can get a good model.


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## Gauss163 (Jun 2, 2016)

HKJ said:


> A simple model with a resistor and capacitor? Then why do you show a model with 4 resistors, 3 capacitors and 1 inductor. Adding enough part and you can get a good model.



Isn't that obvious? They are trying to very accurately model the entire impedance spectrum, which requires further components that can model each of the 5 mentioned components of impedance. That level of accuracy is not needed to roughly explain why voltage sag occurs. 

Note that my initial remark was certainly not meant to _limit _models to a _single _resistor and capacitor. It was very quickly edited (2 months ago!) to clarify that once I realized the possible ambiguity. Did you miss that edit? (you seem to keep quoting the (long nonexistant) unedited version; this only serves to obfuscate the essence of the matter).


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## HKJ (Jun 2, 2016)

Gauss163 said:


> (you seem to keep quoting the (long nonexistant) unedited version; this only serves to obfuscate the essence of the matter).



I quoted your post, but I am glad you admit to obfuscate the matter.


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## Gauss163 (Jun 2, 2016)

HKJ said:


> I quoted your post, but I am glad you admit to obfuscate the matter.



Again you (purposely?) misread. I said nothing of the sort. But by now it is clear that you have no interest in learning about these very interesting models so I won't waste any further time trying to explain them to you.

To anyone that is interested in learning more about internal resistance and impedance, I highly recommend following the links given in the paper I cited. Understanding these models and related matters will _greatly _increase your understanding of Li-ion batteries.


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## HKJ (Jun 2, 2016)

Gauss163 said:


> Again you (purposely?) misread. I said nothing of the sort. But by now it is clear that you have no interest in learning about these very interesting models so I won't waste any further time trying to explain them to you.



Thanks and please do not quote my comments out of context. 
PS: The model you show do not show actual impedance for a cell during discharge. It shows dynamic behaviour, you will have to adjust the component values during discharge. This may be fine for a computer simulation, but not for an easy explanation.


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## Gauss163 (Jun 2, 2016)

@HKJ If you would only read more about these matters then you would learn that the models work fine across the entire spectrum of discharges. I think you have completely missed the point of my recent post. I already gave an excerpt from an exposition from one of the most respected researchers in the field that shows how one can effectively use such simple models when teaching introductions to these matters. The point of my recent post was to supplement that with some links to slightly more complex models, to show how much insight they lend on such matters. I am completed baffled as to why you continue to attack these models. They are very widely used and prove tremendously useful, both at introductory and advanced levels.


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## HKJ (Jun 3, 2016)

Gauss163 said:


> @HKJ If you would only read more about these matters then you would learn that the models work fine across the entire spectrum of discharges.



Then please explain how for resistors in series can model different internal resistance at different charge levels.
If anybody want to check: The article with the above model includes a table with different component values at different charge states, just as I wrote above.
The direct link to the article is: http://jes.ecsdl.org/content/162/8/A1592.full.pdf 




Gauss163 said:


> They are very widely used and prove tremendously useful, both at introductory and advanced levels.



I have no doubt that models are useful also outside universities, but this is a hobby forum where people comes for practical advice, not to get a degree or design a mobile phone power system. This means most people like simple explanations, not research papers.


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## Gauss163 (Jun 3, 2016)

@HKJ There were no claims that the simpler models account for _all _aspects of Li-ion behavior. But there are more sophisticated models that do so (which, in fact, you would have learned if you had delved into the literature I linked when I informed you about the ideas used in the Philips and Tesla fast-charging algorithms) 

By now we've gone far beyond my original remark, which was meant to refer to simple models such as those in the excerpt of Barsukov's introduction that I posted (which some readers remarked that they did find helpful). Those readers who do have an interest in more sophisticated models can chase the links to learn more.


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## HKJ (Jun 3, 2016)

Gauss163 said:


> @HKJ There were no claims that the simpler models account for _all _aspects of Li-ion behavior.



In this thread the discussion was about the increased impedance when the battery is nearly empty, where I say a simple model do not cover it. All your writings has not showed otherwise.
With you postings it is chasing links and maybe sometime hitting something. I do not play that game, I prefer direct links and luckily most people around here has it the same way.


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## Gauss163 (Jun 3, 2016)

HKJ said:


> In this thread the discussion was about the increased impedance when the battery is nearly empty, where I say a simple model do not cover it. All your writings has not showed otherwise.



To better focus the discussion let's recall my original suggestion


Gauss163 said:


> Good choice of topic. It would help to explain a bit about the reason for the voltage drop / bounce, i.e. say something about internal resistance, maybe even mention some simple cell models using resistor(s) and capacitor(s) (the motivation being that it is better to teach them how to fish than to serve them fish on a platter, i.e the better _conceptual _model that the reader has, the easier they can answer such FAQs on their own).



I posted that because there is _not a single word_ about internal resistance (or impedance) in your tutorial, yet this is a crucial component to comprehend in order to gain a better understanding of these matters.

My hope was that you would add some _simple _explanation that gives the reader a rough _qualitative _understanding of the crucial role that it plays here (there is certainly no need for a precise _quantitative _understanding for expositions at this level). Hence my mention of simple models such as equivalent circuit models. I even provided a sample exposition by experts along those lines. But if you prefer some other way to explain these ideas then that is fine too. Anything that lends some intuition on the crucial role played by IR is certainly better than nothing, since lack of knowledge about such is often the major gap preventing new users from properly comprehending such matters.



HKJ said:


> With you postings it is chasing links and maybe sometime hitting something. I do not play that game, I prefer direct links and luckily most people around here has it the same way.



If you are interested in learning about more precise _quantitative _models then you can either start by chasing the links I provided (that's how scientific research works) or you can do some obvious web searches, such as "equivalent circuit model li-ion impedance" where you will find many pertinent papers, e.g. below is an excerpt from a random match that shows how the parameters are chosen in one particular model: Modelling of Li-ion batteries using equivalent circuit diagrams, by A. Rahmoun, H. Beichl,  Przeglad Elektrotechniczny 88(7): 152-156 · December 2011. You can similarly locate many hundreds of articles on other models, with various strengths and weaknesses.


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## Capolini (Jun 3, 2016)

This has been entertaining but ridiculous!

Ones EGO AND PRIDE runs rampant when One is so focused, adamant and concerned about being RIGHT!:shakehead


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## HKJ (Jun 3, 2016)

Gauss163 said:


> I posted that because there is _not a single word_ about internal resistance (or impedance) in your tutorial, yet this is a crucial component to comprehend in order to gain a better understanding of these matters.



And I do simply not see the need for that in this article.
I post a few articles each year, often based on data I have measured. I try to write these article in a not too technical style, i.e. they are not aimed at university students or mobile phone developers, but at people that uses batteries for hobbies.
If you want a more advanced level, you are welcome to post your own articles.


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## Gauss163 (Jun 3, 2016)

HKJ said:


> If you want a more advanced level, you are welcome to post your own articles.



Ok, I'll post an alternative exposition that goes a bit deeper. Honestly, at the start, I thought it was simply an oversight, and that you'd add a couple sentences, and that would be the end of it.


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## HKJ (Jun 3, 2016)

Gauss163 said:


> Ok, I'll post an alternative exposition that goes a bit deeper. Honestly, at the start, I thought it was simply an oversight, and that you'd add a couple sentences, and that would be the end of it.



Remember to put that in a new thread. I will be looking forward to it (I have nothing against more advanced stuff, but it do not below in this thread).


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## Gauss163 (Jun 3, 2016)

Yes, of course it will be a new thread, we've already veered too far off on tangents here. If only you had mentioned at the start that you had made a conscious decision to not discuss internal resistance then we could have avoided the entire tangent. That decision was something I never would have guessed, since you mention IR frequently in other places here.


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## Capolini (Jun 4, 2016)

*TO HKJ:

SORRY FOR POSTING THIS HERE. I DID NOT KNOW ANY OTHER WAY,,,,,,,,YOU USUALLY ANSWER MY EMAILS, HOWEVER THE LAST TWO REMAIN UNANSWERED. COULD YOU PLEASE ANSWER THEM?

MY ONLY OTHER OPTION IS TO START A THREAD WHICH I DON'T WANT TO DO!

,,,THANKS,,,,,,,,,,CAPOLINI 
*


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## HKJ (Jun 4, 2016)

Capolini said:


> *TO HKJ:
> 
> SORRY FOR POSTING THIS HERE. I DID NOT KNOW ANY OTHER WAY,,,,,,,,YOU USUALLY ANSWER MY EMAILS, HOWEVER THE LAST TWO REMAIN UNANSWERED. COULD YOU PLEASE ANSWER THEM?
> 
> ...



Sorry about that, I have been sick this week and not done much. That is also the reason for no reviews most of the week.
I am nearly up to speed again and will take a look on your pm's.


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## MAD777 (Jun 4, 2016)

HKJ said:


> Sorry about that, I have been sick this week and not done much. That is also the reason for no reviews most of the week.
> I am nearly up to speed again and will take a look on your pm's.


Take care of yourself HKJ. We need you!


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## Capolini (Jun 4, 2016)

HKJ said:


> Sorry about that, I have been sick this week and not done much. That is also the reason for no reviews most of the week.
> I am nearly up to speed again and will take a look on your pm's.




*GLAD YOUR FEELING BETTER! THANKS HKJ,,I APPRECIATE THE REPLY!*


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## ven (Jun 4, 2016)

MAD777 said:


> Take care of yourself HKJ. We need you!




+1 

Get well soon


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## Gauss163 (Jun 4, 2016)

ven said:


> +1 Get well soon



A little cellular advice often works wonders for me:


Dr. Li Ion said:


> to improve health and _internal resistance_, avoid getting too charged up while hot under the collar. :hairpull:



But, seriously, best of luck on a fast recovery charge.


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## P_A_S_1 (Jun 8, 2016)

Just took an rcr123 out of one my lights that was so drained it wouldn't register on my volt meter. I thought I had a primary in there and purposely ran it down to nothing. Throwing it on the Cottonpicker charger the first reading was 2.6v (oh boy). I just read this thread in regards and if I understand correctly I should be good. Thxs for posting this thread, it's helpful.


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## Phlogiston (Jun 11, 2016)

P_A_S_1 said:


> Just took an rcr123 out of one my lights that was so drained it wouldn't register on my volt meter. I thought I had a primary in there and purposely ran it down to nothing. Throwing it on the Cottonpicker charger the first reading was 2.6v (oh boy). I just read this thread in regards and if I understand correctly I should be good. Thxs for posting this thread, it's helpful.



If your RCR123 has a protection circuit, and you put it on the charger immediately after the light shut off, you should be fine. The deep discharge will knock a few cycles off the cell's service life, though.


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## wimmer21 (Aug 17, 2016)

Great thread! The back-n-forth between experts forced me to read everything carefully and led to me learning a bit. Even though some of the interaction might have been annoying to some, I actually think it made what would've been an excellent and informative thread on its own, even better. 

Reminded me of the Battle of Wits from The Princess Bride. Inconceivable!


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## Swedpat (Aug 18, 2016)

Thanks for another great thread HKJ,

I have to say that this matter is as well interesting and important but I still don't understand all details. Sometimes it seems a bit contradictory. While the illustrations from LiIon handbook defines over discharging as <2,5V you mean it's below 3,3-3,6V depending on the model, as I understand it. And if the remaining capacity of a cell is 0% it logically should mean that it can't provide any power at all to a light. Still it seems possible to run it even lower...

Anyway; I am very pleased with the use of Li-Ion cells especially when these can replace or be a complement to CR123s in a light. Especially I like the 16650 format which is an excellent choice for many 2xCR123 lights who can't take 18650(or 17670). 

Regarding the capacity of Li-Ions my personal intention is to make use of it. If I get 3500mAh cells I do it because they provide longer runtime than lower mAh models. 
If regulated runtime for a certain light at a certain brightness level is 90min I find no reason to never run it more than, for example, 30-40min before recharge(like I know some flashlight users are careful to always do). If so I could get cheaper 2600mAh cells instead and they do the same job. And if the voltage of the cell now and then becomes a bit lower than it should be for the sake of keeping the lifetime in cycles as high as possible it's not the whole world. It will still work for several years.
Of course I find no reason not to fully charge a cell before use even if it's not runned low, when I have time and possibility to do it. 
I just mean that I feel it can sometimes go a bit too far to never run the cells half full or less. 

I have mentioned it before that I find it strange that the over discharge protection of Li-Ion cells actually is not a true over discharge protection. If it would it should not be a problem to run the cells until the protection kicks in. For example: if a cell should not be discharged below 3,3V the protection SHOULD kick in at that level.

Just my honest thoughts.


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## HKJ (Aug 18, 2016)

Swedpat said:


> While the illustrations from LiIon handbook defines over discharging as <2,5V you mean it's below 3,3-3,6V depending on the model, as I understand it. And if a the remaining capacity of a cell is 0% it logically should mean that it can't provide any power at all to a light. Still it seems possible to run it even lower...



There is a couple of points:

 Is the cell loaded, this can mean a significant voltage different, especially when the cell is nearly empty.
Is your goal is maximum lifetime: Stay above the highest value.
Is your goal is maximum capacity you can go a bit lower, but the difference in capacity is rather small.
Is your goal to stay safe and you do not care about lifetime you can go down to the lowest value.
Going below the low value may make the cell dangerous, but will not always do it.


Cell ratings is usual based on getting a decent lifetime, then on capacity (The difference is rather small).


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## Swedpat (Aug 19, 2016)

HKJ said:


> There is a couple of points:
> 
> Is the cell loaded, this can mean a significant voltage different, especially when the cell is nearly empty.
> Is your goal is maximum lifetime: Stay above the highest value.
> ...



Thanks for answer!

Sorry if I am dumb here, but with lowest and highest value, do you mean 3,3 vs 3,6V?


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## HKJ (Aug 19, 2016)

Swedpat said:


> Sorry if I am dumb here, but with lowest and highest value, do you mean 3,3 vs 3,6V?



3.3V or 3.6V is not very significant, many batteries can be discharge down to 2.5V.


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## Swedpat (Aug 19, 2016)

HKJ said:


> 3.3V or 3.6V is not very significant, many batteries can be discharge down to 2.5V.



Ok, thanks! 

Then I understand I don't need to be very worry about the exactly voltage unless it does not go very low. Usually my Li-ions have not been down to 3V unloaded before recharge.


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## Collins (Aug 20, 2016)

HKJ said:


> 3.3V or 3.6V is not very significant, many batteries can be discharge down to 2.5V.



Reading through all of your LiIon/NiMH charger reviews.

Do you have top 5 lists or maybe top 3 lists of your ranking best to least best charger? 

i.e. top 5 or top 3 lists of 4-bay LiIon/NiMH chargers?

Maybe a list that includes chargers with fans, and a list without fans? As fans are a huge turn-off for a lot of people.

Been reading your reviews trying to decide on a 4-bay charger without a fan as I need it quiet in bedroom during the night.

Thanks


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## ven (Aug 20, 2016)

Sure the Xtar xp4 panzer does not have a fan, will do nimh as well. 4 bays at 1a each!.
Pretty good value, no voltage readout though..............

As much as it can be an inconvenience, it does help keep things cool and under control,especially with chargers that have higher rates and discharge options. To help keep them fairly compact, its kind of part of the package as with hobby chargers.


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## KeepingItLight (Aug 22, 2016)

Instead of 4-bay charger, consider getting an analyzer/charger. The *Opus BT-3100* and *LiitoKala Engineer Lii-500* both got good reviews.


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## samgab (Aug 27, 2016)

Nice info kept simple for people new to li-ion cells etc. Cheers HKJ. 
I wanted to mention too, that the reason for not over-discharging li-ion cells on a regular basis is not only because it reduces the usable life of the cell, although that is certainly a negative effect of over-discharging. Another big reason is the safety concerns. Sometimes it happens over time, sometimes it can happen immediately, but when this chemistry cell is over-discharged - without going into chemical details - it causes the copper metal (which is used as the current collector at the negative electrode) to dissolve into the electrolyte material inside the battery, and then when it is recharged again the copper can redistribute itself again inside the battery in such a way that it causes a short inside the cell, which can then cause thermal runaway, start a fire etc when the cell or battery is recharged. Again, this doesn't happen when over-discharging, but it creates a situation where the battery is no longer safe when subsequently RE-charged. You might be lucky a hundred times and nothing bad happens, or it might happen the hundredth time recharging, the 50th time, or even the first time recharging after an over-discharge. 

So what I'm saying, in a nutshell is: There is also the safety factor involved in over-discharging li-ion cells or batteries. It can be dangerous and should be avoided, not just for the longevity of the cells, but also for safety. Stay safe out there! 






-source: Lithium-Ion Batteries Hazard and Use Assessment paper, Fire Protection Research Foundation.


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## recDNA (Jan 22, 2019)

My Keepower 16650 protected battery was at 2.65 volts when my flashlight dropped to only low mode. It may of course have been lower and bounced back to 2.65 volts by the time I checked it. Anyway is the battery safe to continue charging and using or should it be recycled due to over discharge?


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## archimedes (Jan 23, 2019)

recDNA said:


> My Keepower 16650 protected battery was at 2.65 volts when my flashlight dropped to only low mode. It may of course have been lower and bounced back to 2.65 volts by the time I checked it. Anyway is the battery safe to continue charging and using or should it be recycled due to over discharge?



How long was it undervolted (overdischarged) ?

There is a spectrum of risk. Personally, I am not comfortable with cells that have been under 3V for any appreciable duration.

https://lygte-info.dk/info/BatteryLowVoltage UK.html

https://www.mpoweruk.com/lithium_failures.htm


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## ven (Jan 23, 2019)

I would put on slow 0.25a charge and keep an eye on it. I have had cells drop less and been fine. Everyone has their own safety margins, i try like archi to not let them get bellow 3v. However many cells have a min spec and measured from 2.5v. So unless bellow 2.5v and near 2v for a period, I would charge and monitor . All should be fine imo. Even at 2v, as long as not left for a long period, will still be fine. 

It must be near the PCB min V? So if it’s not tripped(would of course read 0v)I would keep and use .


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## usdiver (Jan 23, 2019)

I m not sure if I posted previously but my Batteries in my HDS have dropped well below 2.75 and still charged up ok. In my first light Tomahawk 425 on the other hand the imr s have dropped down to 0% according to the vp4 dragon and still charged up ok. .5 amp is minimum recharge .25 would be preferred


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## Nev (Jan 23, 2019)

I have 8 PKcell 14500's ,I used one of them in my LUMINTOP tool AA which doesn't have LVP & I noticed I drained the cell to 1volt something ( it was last year & can't remember the exact voltage) but I charged it up & it's been fine. I did a discharge test on all 8 cells the other day thinking I would be able to spot which one it was , but they all tested about 850mah & all 8 cells have similar IR measurements ,so I conclude no damage was done , I shoulda marked that particular cell but didn't , I have no idea now which one it was but there all fine after about a year.


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## WalkIntoTheLight (Jan 23, 2019)

According to the Samsung 30Q spec sheet, it says you should not recharge a cell that is below 1.0v. Charging between 1.0v and 2.5v should be done slowly, until it's above that voltage.

But the spec sheet makes no mention of _how long_ a battery can be left in a severely discharged state. If it's more than a few days sitting near 1v, I'd probably consider it unsafe.


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## recDNA (Jan 23, 2019)

ven said:


> I would put on slow 0.25a charge and keep an eye on it. I have had cells drop less and been fine. Everyone has their own safety margins, i try like archi to not let them get bellow 3v. However many cells have a min spec and measured from 2.5v. So unless bellow 2.5v and near 2v for a period, I would charge and monitor . All should be fine imo. Even at 2v, as long as not left for a long period, will still be fine.
> 
> It must be near the PCB min V? So if it’s not tripped(would of course read 0v)I would keep and use .


The PCB never tripped. I only discovered the problem when a seldom used flashlight only turned on low with no access to other modes. I would guess it was in that state for days not weeks. The pcb should trip at 2.5 but on very low output I wasn't sure it would work. The battery did recharge uneventfully to 4.19 volts. I guess I will trust that the pcb would have worked had the battery dipped below 2.5 v. From reading about copper dissolving in HKJ explanation I guess the battery is just as dangerous in the drawer as it would be in the flashlight. I try to never allow batteries to dip below 3.3 volts so I have little experience with undercharged cells. Apparently once a runaway reaction begins the pcb isn't of any use.


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## Nev (Jan 23, 2019)

I found this quite interesting 
https://youtu.be/sRwoYJyjZNo


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## flatline (Jan 23, 2019)

I normally use low output, so I don't expect much voltage recovery at all. As such, I tend to throw my cells in a charger before they get below 3.6v.

--flatline


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## recDNA (Jan 23, 2019)

recDNA said:


> The PCB never tripped. I only discovered the problem when a seldom used flashlight only turned on low with no access to other modes. I would guess it was in that state for days not weeks. The pcb should trip at 2.5 but on very low output I wasn't sure it would work. The battery did recharge uneventfully to 4.19 volts. I guess I will trust that the pcb would have worked had the battery dipped below 2.5 v. From reading about copper dissolving in HKJ explanation I guess the battery is just as dangerous in the drawer as it would be in the flashlight. I try to never allow batteries to dip below 3.3 volts so I have little experience with undercharged cells. Apparently once a runaway reaction begins the pcb isn't of any use.


Yes I did too. Thanks! Sounds like our chargers should all trickle until battery reaches 3 volts. I know mine doesn't because at .25 amps it very quickly charged the battery from 2.65 volts to 3 volts but it actually took hours to get to 4.19. This morning the battery is 4.16 volts. I will check it tomorrow to see if it continues to drop. The video suggested that might indicate a slow self discharge due to some tiny copper channels (Bad). If it stops dropping battery should be ok ( according to video). I didn't get the part about -12% He keeps saying how bad it is if battery gets to -12%. -12% of what and how do you measure it?


Nev said:


> I found this quite interesting
> https://youtu.be/sRwoYJyjZNo


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## archimedes (Jan 23, 2019)

The problem is, as I understand it, related to the creation of microscopic sharp metallic spicules or "needles" ....

Once created, these do not resolve, and can even grow (under certain conditions)

If these metal needles pierce the onion-like wrapped layers of the battery, much badness can result.

So my concern is that cell can never really be fully trusted again, even if it "makes it" through a cycle or two of (gentle) charging.

Although the riskiest event is charging, there may be tiny internal micro-shorts which could worsen and heat up under heavy drain, and the cell may be more vulnerable to physical shock due to the presence of those sharp internal structures.

Even at rest, if the needles continue to slowly grow, there could eventually be a problem.

So I try to stay well within the conservative safety range.


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## peter yetman (Jan 23, 2019)

usdiver said:


> I m not sure if I posted previously but my Batteries in my HDS have dropped well below 2.75 and still charged up ok. In my first light Tomahawk 425 on the other hand the imr s have dropped down to 0% according to the vp4 dragon and still charged up ok. .5 amp is minimum recharge .25 would be preferred


Just for you, I did a little test.
I discharged an AWT 16340 in my Xtar Dragon at 1 amp. When the charger read 0% the voltage under load was 3.0v. After a little rest off load the voltage was 3.25v.
I put the cell in an HDS and after a few seconds on full power it started the low voltage flash. Immediately off load the voltage was 2.45v and rising, it stabilised at 2.8v
I've rounded the numbers up and down, and bear in mind that the figures are only as accurate as my charger and meter.
Of course the charge will only show 0% at and below 3.25 off load voltage. So the cell could be anything below 3.25v
P


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## Nev (Jan 23, 2019)

recDNA said:


> Yes I did too. Thanks! Sounds like our chargers should all trickle until battery reaches 3 volts. I know mine doesn't because at .25 amps it very quickly charged the battery from 2.65 volts to 3 volts but it actually took hours to get to 4.19. This morning the battery is 4.16 volts. I will check it tomorrow to see if it continues to drop. The video suggested that might indicate a slow self discharge due to some tiny copper channels (Bad). If it stops dropping battery should be ok ( according to video). I didn't get the part about -12% He keeps saying how bad it is if battery gets to -12%. -12% of what and how do you measure it?



I'm not sure , he said he put a link to the article he read under his video , I didn't look at it but I think he said it was sciency.


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## WalkIntoTheLight (Jan 23, 2019)

Nev said:


> I'm not sure , he said he put a link to the article he read under his video , I didn't look at it but I think he said it was sciency.



IIRC, this study was brought up on the forums awhile back. It claims that lithium-ion cells are okay until they are _reverse charged_ by up to 12% of their capacity. That is, their polarity would be reversed. This can happen in multi-cell series configurations, if using cells with different capacities or states of charge.

IMO, I wouldn't trust a cell that was so badly discharged its polarity was reversed.


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## recDNA (Jan 23, 2019)

Nev - thanks for going to all that trouble!

I never use multiple li ion batteries in a flashlight so I do avoid that problem. Most of my li ion batteries are protected. I only use unprotected cells in the new Zebralights.

I've used li ion batteries since the year 4sevens opened whenever that was. I've only had 3 thermal runaway incidents and only 1 vent (no flame). All 3 were single protected cells of very high ratings and popularity. All 3 had this event when the flashlight was off! In one case I think the cell was too long for the flashlight and it got crushed enough to go into thermal runaway right away. I threw it out on the lawn and it partially melted but I didn't see any vent. The one that vented was in a low power flashlight that had been used for a few minutes then left in an off state on a shelf. For no apparent reason it vented. Scary but nobody hurt. The 3rd case the cell had melted inside the off flashlight and I didn't find out until flashlight failed and I attempted to take out the battery. I have no idea what happened but the flashlight was in a coat pocket and could have burned my house down. None of the cells were abused nor allowed to drop below 3 volts. All were less than a year old. My anecdotal experience gives me no insight at all into what contributed to high quality high rated expensive protected batteries going poof.


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## Nev (Jan 23, 2019)

recDNA said:


> Nev - thanks for going to all that trouble!
> 
> I never use multiple li ion batteries in a flashlight so I do avoid that problem. Most of my li ion batteries are protected. I only use unprotected cells in the new Zebralights.
> 
> I've used li ion batteries since the year 4sevens opened whenever that was. I've only had 3 thermal runaway incidents and only 1 vent (no flame). All 3 were single protected cells of very high ratings and popularity. All 3 had this event when the flashlight was off! In one case I think the cell was too long for the flashlight and it got crushed enough to go into thermal runaway right away. I threw it out on the lawn and it partially melted but I didn't see any vent. The one that vented was in a low power flashlight that had been used for a few minutes then left in an off state on a shelf. For no apparent reason it vented. Scary but nobody hurt. The 3rd case the cell had melted inside the off flashlight and I didn't find out until flashlight failed and I attempted to take out the battery. I have no idea what happened but the flashlight was in a coat pocket and could have burned my house down. None of the cells were abused nor allowed to drop below 3 volts. All were less than a year old. My anecdotal experience gives me no insight at all into what contributed to high quality high rated expensive protected batteries going poof.


You're very welcome.


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## Nev (Jan 23, 2019)

I think this is the article he was referring to
https://www.youtube.com/redirect?ev...3UMSzdiE369M_WqJ8MTU0ODM0MzMzOEAxNTQ4MjU2OTM4


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## Nev (Jan 23, 2019)

It's definitely sciency ;-)


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## WalkIntoTheLight (Jan 23, 2019)

recDNA said:


> Nev - thanks for going to all that trouble!
> 
> I never use multiple li ion batteries in a flashlight so I do avoid that problem. Most of my li ion batteries are protected. I only use unprotected cells in the new Zebralights.
> 
> I've used li ion batteries since the year 4sevens opened whenever that was. I've only had 3 thermal runaway incidents and only 1 vent (no flame). All 3 were single protected cells of very high ratings and popularity. All 3 had this event when the flashlight was off! In one case I think the cell was too long for the flashlight and it got crushed enough to go into thermal runaway right away. I threw it out on the lawn and it partially melted but I didn't see any vent. The one that vented was in a low power flashlight that had been used for a few minutes then left in an off state on a shelf. For no apparent reason it vented. Scary but nobody hurt. The 3rd case the cell had melted inside the off flashlight and I didn't find out until flashlight failed and I attempted to take out the battery. I have no idea what happened but the flashlight was in a coat pocket and could have burned my house down. None of the cells were abused nor allowed to drop below 3 volts. All were less than a year old. My anecdotal experience gives me no insight at all into what contributed to high quality high rated expensive protected batteries going poof.



Wow, 3 thermal runaway incidents with apparently no cause? That's scary.


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## recDNA (Jan 23, 2019)

WalkIntoTheLight said:


> Wow, 3 thermal runaway incidents with apparently no cause? That's scary.


Over the course of many years. The funny part is I used to use X-fire batteries and never had a problem with them. It was my good batteries that went bad. One was my fault. The battery was too long so I shouldn't have tried to use it. The one that popped after using it in 1 amp flashlight I suspect was the fault of the flashlight itself. Had to be a short. Of course there could have been an unnoticed tear in the wrapping over the protection strip. The one in my coat pocket may have occured when the 3 amp p60 was turned on accidentally in my coat and overheated. I've used dozens of batteries uneventfully for years. I own too many flashlights and too many batteries! LOL

I haven't had any more battery problems in 5 years so it's been a while since those events.

Funny thing is I had a Note 7 and never had a problem with it. I hated to give it back!


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