Li-ion How low is too low?

kbuzbee

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Okay, maybe stupid question but it came up so I'd like to know.

I know you're not supposed to over discharge Li-ion batteries as it shortens their life and at some point becomes dangerous. At what point do you cross that line?

Here's what happened. I left an ET 16340 in a V11R. It was pretty full (4.1v) A couple days later I went to turn the light on. Nothing. Tested the battery, it read 1.1v. I have no idea what happened but probably it was left on (or accidentally activated) at the very lowest setting and just ran down.

So, how low is it safe to recharge Li-ions? Does it differ with ICR/IMR/IFRs? I know running them low shortens battery life and I usually top them off around 3.8v but when does it become dangerous? (Or does it?)

Thanks!

Ken
 

HKJ

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That battery is dead.
The lowest voltage depends on chemistry. The Panasonic 3100/3400mAh can be discharged much lower than a 2600mAh battery, before anything happens.
The first that happens when you discharge to much is that the battery looses capacity, this can easily be 50% capacity. If you go lower the battery may also get unstable.
 

HKJ

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But is there a cut off to make that call? 2v? 3.5v?

According to some literature I have seen the cell get dangerous below 2 volt.

I have seen lost capacity at 2.5 volt, but never at 2.8 volt.

The 2.8 volt is the low value I uses for all my tests.
 

kbuzbee

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The 2.8 volt is the low value I uses for all my tests.

Excellent! Thanks! That's what I'll use, then.

By the way, have you gotten a Nitcore D4 to review yet? I really enjoy reading your reviews even if a lot of it goes over my head.

Ken
 

HKJ

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By the way, have you gotten a Nitcore D4 to review yet? I really enjoy reading your reviews even if a lot of it goes over my head.

Not yet, but Nitecore has promised to send me one.
Until then I am working on i2 and i4 in 2014 version
 

markr6

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Cool. Looking forward to reading them.

Me too! I'm considering a cheap, small, NiMH/Li-Ion charger that I can keep in my car for emergencies (rarely/never used). So the i2 has my attention even though it's pretty slow.
 

Tmack

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The x star brand has some single lithium ion charger off mini usb for like $5

I use it with my solar setup if I only need 1 cell.

Otherwise my solar charger will easily rum my i4.
 

Kueh

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From what I've seen and read, it's very possible to revive that cell. It involves using a nimh or nicd charger with low current output, 100mA or less. You charge the cell (in a fire /explosive safe container) for a lengthy period, maybe a few days. You need to monitor the cell voltage regularly for it to rise up to around 3 volts. At that point, you can use a lion charger. There need to be rest periods in between attempts. I have seen videos and read articles stating that the process works sometimes. I have not seen or read anything saying that their batteries had exploded or leaked. Just that their attempts didn't work.
 

kbuzbee

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From what I've seen and read, it's very possible to revive that cell.

Okay, but would the cell be safe to use then? Or possibly just run with diminished capacity after that?

Ken
 
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m4a1usr

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Good information, thanks!

Is there any way to test a cell to determine if it's ever been over discharged?

Ken
Yes. An internal resistance measurement would indicate cell condition but you would need a 4 wire DMM to measure it plus you would need to know what that initial value when the cell was new to use as comparison.
 

Gauss163

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kbuzbee said:
Is there any way to test a cell to determine if it's ever been over discharged?
Yes. An internal resistance measurement would indicate cell condition but you would need a 4 wire DMM to measure it plus you would need to know what that initial value when the cell was new to use as comparison.

High internal resistance does not imply that the cell has been over-discharged. Rather, it is a normal consequence of cell aging (e.g. for a typical Li-ion the internal resistance increases about 60% after the first 100 cycles).
 

kbuzbee

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The key is LOW current charging. It is just one cell. It depends on how much effort that you want to put into reviving it.


Thanks! Great video. At this point I'm not too concerned with reviving this particular cell but I have a few cells I've acquired from folks over time and I'm more interested in learning whether they are safe to use. Would an MBT-1 tell me that?

Yes. An internal resistance measurement would indicate cell condition but you would need a 4 wire DMM to measure it plus you would need to know what that initial value when the cell was new to use as comparison.

Is it of any use if you don't know the initial value?

Ken
 

Kueh

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A quick look at the MBT-1 suggests that it only tests capacity.

The longer that a battery remains in a discharged condition will result in damage to that battery.
 

kbuzbee

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A quick look at the MBT-1 suggests that it only tests capacity.

So (and I realize the MBT-1 doesn't give mAh - I don't really understand what it's six LEDs indicate) but if it did... If a battery is rated at 750 mAh but it reads 300 mAh it's probably been over discharged at some point (or is just getting really old?)

The longer that a battery remains in a discharged condition will result in damage to that battery.

With a long time being? An hour? A day? Three days? Just trying to get a handle on this stuff.

Keen
 

THE_dAY

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Taken from Battery University:
Do not recharge lithium-ion if a cell has stayed at or below 1.5V for more than a week. Copper shunts may have formed inside the cells that can lead to a partial or total electrical short. If recharged, the cells might become unstable, causing excessive heat or showing other anomalies. Li-ion packs that have been under stress are more sensitive to mechanical abuse, such as vibration, dropping and exposure to heat.

Basically there is some crystallization formed inside the cell from being discharged too low, the cell then can be dangerous when trying to recharge.
There might not be any signs early on but over time that cell can become a hazard.
 
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