IMR over-discharge

ScottJ

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I have been EDCarrying a flashlight (Nitecore EC11) the last couple of weeks that was designed to accept 18350 IMR batteries. I have two such batteries (same brand, Nitecore, 700mAh) and I've had the setup for a couple of years, just never got around to carrying it daily.

Unfortunately, the light is a side-switch type, and the switch is a little too touchy for pocket use. So three times now, the light's gotten turned on in my pocket and stayed on. To my disappointment, the flashlight manufacturer did not include a low voltage shutdown circuit, which in my opinion is crazy if the light's designed for rechargeable lithium. So, yeah, three times my battery has been discharged all the way down to about 1.2-1.4 volt.

All three times, the battery has accepted a charge and returned to full voltage. All three times the battery APPEARS unharmed. But the question, given the stuff I've seen about overdischarging and damage to cells, is are these cells SAFE to use now, even though they seem fine? The last thing I want is a flashlight blowing up in my pocket because there's separator damage to these cells.

There's an adapter (included) that'll let me use CR123A primaries in this light instead, if I choose to continue carrying it and the IMRs are no longer trustworthy. Or I may just not carry it, or carry it locked out when I do (by loosening the tailcap).

Any advice appreciated.

Scott
 

XD9

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Interesting, To my knowledge the EC11 does have LVP. At any rate.... The EC11 can be locked so it does not turn on in your pocket. From on -> Hold both buttons until the light flashes and it goes in to lock mode. Same for unlocking it....
I am not sue which charger you have that allows you to recover your Battery's... Bad IMR battery's require a especial cycle to be return back from the dead... But dead means 0v so I think the EC11 is doing its job and triggering LVP :D
IMO Your battery's are fine... But dont take my word for it and make your own decision ;)
 

archimedes

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My understanding is that the risk of overdischarged Li-Ion cells increases over time ... in other words, the longer (and lower) it has been undervolted, the greater the danger.

Personally, I would be uncomfortable continuing to use cells that had been under 2.5V (and especially < 2.0V) for any significant length of time.
 

tabetha

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I don't know if I am getting confused but I inadvertently left my S1 Baton on high and out of sight forgetting about it it went "flat", it showed either 0.06 or 0.6V, can't remember which put in my opus charger and not recognised as cell inserted, put in my xtar vc4 for 10 secs then in opus and all fine, the cell was a 550mah olight RCR123 5C, working perfect now, most of mine get taken down to dead before recharge
 

peter yetman

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To be honest, if they were my cells I'd bin them. What are two new cells going to cost you? certainly not as much as the damage they could possibly cause.
P
 

WalkIntoTheLight

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Check your cell to see if it's been damaged.

1. It should take a full charge to 4.20v.

2. After resting a few hours, it should hold a voltage above 4.17v.

3. After resting for a week, it should only lose about 0.001v per day.

The last point is critical. It should determine whether or not your cell has developed any spikes inside that could lead to an internal short.

If it tests okay, it probably is okay. I've read reports that suggest lithium-ion cells don't really suffer from dangerous damage unless they're reverse-charged (below 0v). However, they are likely to lose capacity if you drain them below 2.5v for very long.
 

tabetha

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It takes a full charge to 4.2, and after 1 day was still 4.19, it says it is protected from over discharge, over charge short circuit etc, so I expect when it went off it went into "protection" mode, it has been recharged 6 or 7 times since perfectly and still beats all my other cells of that size, I have always relied on the protection to do "what it says on the tin" and never had issues, but my dad had a Li cell or Lipo swell up big time even though it wasn't in use at time.
I don't know what olight choose voltage wise for the cut out but assume it is appropriate.
 

kpatz

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If it's a protected cell it won't over-discharge. Instead the protection circuit will disconnect the cell, which is why you got the "completely dead" near zero voltage when you measured it. Once you charge it again the protection resets.

For an unprotected cell, it depends on how far it's drained and for how long. If it's moderately over-discharged (say to 2.2V) for only a short time, it will probably be ok. If it's lower or for a longer time, there's a better chance for damage, in which case you'd want to check it using WalkIntoTheLight's technique. Also, make sure the cell doesn't get overly warm/hot while charging, as that's a sure sign it's bad as well.
 

Modernflame

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I would recycle them without any delay. If the discharge had terminated somewhere north of 2v, I would test and monitor them, but 1.2v is much too deep.
 

recDNA

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Absolutely discard them. No way to know if chemistry is screwed up and will eventually short even with battery not in use! Very likely it will short when you're charging it some day. Recycle.
 

SilverFox

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Hello ScottJ,

Welcome to CPF.

If there is damage to the cells you should recycle them.

If you have no way of testing your cells, it would be worthwhile recycling them in order to be safe.

If you have a way of testing them, the picture changes.

On one hand you can recycle them and move on. On the other hand if they charge up, hold voltage overnight, and have a discharge capacity within 80% of what they had when they were new, the evidence is that very little damage was done to the cells and you can probably continue to use them.

Tom
 

recDNA

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Heck I throw mine away if they go below 2.5V. That means under load they were actually even lower. I don't even like using unprotected batteries (although I do) so I am likely more careful than most.
 

HKJ

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The lower limit for LiIon is around 2 volt according to the manufactures, I wrote a bit about it here:
http://lygte-info.dk/info/BatteryLowVoltage UK.html

At 2V you might damage the cell, but it will not make it dangerous, only loose capacity.

Protected cells is another story, they can be at zero volt without any damage, because it is the protection that has disconnected the battery, i.e. it is not the actual battery voltage you are measuring. I did also test some protections: http://lygte-info.dk/info/DischargeProtectionTest UK.html
 

Gauss163

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Check your cell to see if it's been damaged [...]

But there are no user-level tests that always work to detect overdischarge damage. There's no way to predict whether or not it will lead to problems at some future time. Severely overdischarged Li-ion cells should be treated like ticking bombs with timers of unknown duration.
 

Gauss163

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[...] On the other hand if they charge up, hold voltage overnight, and have a discharge capacity within 80% of what they had when they were new, the evidence is that very little damage was done to the cells and you can probably continue to use them.

That's dangerous advice. Why do you believe the above test implies that little damage was done and they are safe for continued use?
 

SilverFox

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Hello Gauss163,

Stored energy is dangerous... Any advice on using stored energy is dangerous advice...

Over discharging damages the balance of the electrolyte inside the cell. It may also damage the electrodes in the cell. This results in reduced voltage after charge along with reduced capacity.

Keep in mind this involves single cell use so the discharge is limited to a maximum of 0 V and the cell won't be driven to - voltage by other cells.

What are your suggestions on ways to determine cell health?

Tom
 

Gauss163

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^^^ One of the primary dangers of overdischarge is copper dissolution, which may lead to dendrites and internal shorts.. This is not necessarily recognized by your proposed test.
 
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Gauss163

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^^^ As I said above, there is no known foolproof method for a consumer to test if a severely overdischarged Li-ion cell is safe to continue to use. Some of the tests proposed above may help to recognize moderate internal shorts that have already formed. But they won't reveal other internal damage, e.g. dendrites that haven't yet grown large enough to pierce the separator. These may continue to grow during use - which could lead to internal shorts at some future date, with possibly little if any advance warning signs.

While there have been improvements over the years to reduce such risks (e.g. browsing patents reveals chemistry improvements to suppress copper dissolution, and ceramic separators to suppress or localize internal shorts) there is no way to know how those improvements affect overdischarge safety of particular cell models since this information is usually proprietary and not made available to the general public.

As such I think we should err on the side of caution and generally consider severely overdischarged cells to be subject to possibly greatly increased safety risks. In particular, I think it is highly reckless to propose tests that rule out such risks without having any strong scientific evidence supporting such tests. Surely we don't want to see future posts like "I followed xyz's method to test if my overdischarged 18650 was safe and it passed, but 2 months later it exploded while charging and I suffered severe injuries..."
 
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SilverFox

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Hello Gauss163,

Now you have changed the discussion from overdischarged to severely overdischarged...

This paper goes into the difference. It is interesting to note that for these particular cells "The cells under overdischarge that were terminated in Stage I exhibited no discernible changes in properties..." Stage I involved discharging down to 0 volts.

Everything I read, and my personal experience backs this up, indicates that when you interfere with the balance of the electrolyte or damage the electrodes you end up with reduced capacity and voltage bleed off after charging. There are other things to look for such as over heating during charging and swelling but that should be a part of everyone's charging regime. In the future additional test methods may emerge but for now I use what I have available.

Now if we were talking about a multi cell battery pack, I am totally with you. Recycle the whole pack and move on. With multiple cells connected in series you can drive a single cell to be severely overdischarged and that can cause problems.

Remember this discussion involves a single cell driven down to around 1.2 volts.

Tom
 
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