18650 gets super hot when charging

I have a battery that sometimes get very hot when charging and would have a voltage of 3.8-3.95V coming off the charger, so i kept an eye on it and if it warmed up i would pull it, drain it a bit and put it back on the charger and it would fully charge and work fine. This has been happening for the last couple months, maybe once every 3 weeks or so (probably 3-4 charges a week), yesterday i was using it, and tossed it on the charger while i was doing some house repair and went on to another battery (i needed constant light), when i took a break 2 hours later and checked on the battery it was very hot, almost hand burning, my IR temp reader said it was 80ºC, so i pulled it, it was at 3.85V, i almost drained it, tossed it back on the charger 30 mins ago, and its warm already its at 3.9V.

Any thoughts, i’ve never had it heat up this hot or heat up two charges in a row, and both times the charger was still feeding current into it, it had not terminated. Its working in my Convoy S2 no problem right now

Dosen’t sound very safe…I wouldn’t keep using that cell.Please don’t blow yourself up Bort!

I had an old trustfire flame from 2009 which showed a similiar but weaker thing. It got warm in the charger. I tested capacity and it also was just half the capacity when it was new so I don’t use it anymore, I will strip the protection and recycle it when I have time.
I guess that happens if the cell gets old and get higher resistance or so…

Which cell is it and how old is it?

Its a sanyo laptop pull, so i don’t know how old, if anyone has a link to deciphering the code i can check.

I can’t check its capacity but i suspect its about half of its new capacity, its a purple ring cell

throw it out and fast, no need to do harm to anything you own or yourself. if you live in the states, i will send you a few 18650’s(unprotected)

Throw it carefully wrapped into a proper recycling bin — because once a cell is unreliable, it may take some time sitting quietly building larger crystals before a crystal pokes a hole in the membrane between the chemicals. Seriously. You put others at risk.

I know that’s what others meant to say by ‘throw it away’ — I’m just belaboring the obvious:

When the chemicals mix through a hole poked by an internal crystal, they react fast — the battery starts to get hotter and vents its liquid flammable contents and may catch fire. This can happen after some time delay.

The only Li-ion I’ve personally ever found vented had been in a metal box for several months, where I’d put it after it seemed not to hold charge well. Opened the box and found a brown stain all around the positive end vents. And that was a tiny little CR2 rechargeable, all alone, probably too small to get too hot and burn — I got lucky.

Just some really good advice bort: stop wasting your time, risking your health and that of those around you while playing with wasted cells. From your prior posts and level of participation on this forum, you should know this far more than most anyone here. :wink:

I am not as cautious as I should be with my 18650s, but this is a clear indication that the cell should be disposed of assuming the charger has been confirmed to be working properly.

Its funny the answers i’m getting now are what i expected last year when it happened for the first time and i posted on BLF and was told its no big deal just watch the cells while they charge and pull if warm.

I will drain and toss it, i have 5 more from the pack so i am good, can it still vent and flame under 3V if i fully drain it in the light before disposal?

Recycle the cell properly.

Saving a few bucks isn’t worth the risk in my opinion.

I agree. recycle it but what rate is the charger charging?

It charges at 1A, its a ML102, it terminates at 4.11V so the battery has never been fully charged since i’ve owned it (about a year)

I’m not sure if this is the safest thing to do, but I usually wire a suitable value resistor across a cell I’m going to recycle and chuck it in an ammo can to discharge for a few days.

By the way, if you need a couple of 18650s in a hurry, I’ve still got a few unused Samsung pack pulls which I can spare, just shoot me a PM if you need them.

I don’t think it will be a problem draining it in the light, its at 3,73V so almost dead anyways, i might do an experiment that i’ve always wanted to do and see what happens if i leave it running after it hits the low voltage cutoff at 3V, seeing what voltage the LED will stop running at

Do they hold voltage ?

Do they charge all the way up to whatever your charger normally charges cells to .?

Do they get hot when charging ?


In almost every laptop pack thats a used pack there are cells that are obviously hurt more than others .

I look for a voltage drop after a day ....after a few days ....a week ....a month etc .

On each cell if they are at all questionable or from a used pack I'll mark day charged and what voltage .if a cell charges up to 4.2 I usually expect it to drop to 4.19 in a matter of hours?/mins.If it's at say 4.14 in a couple weeks after just sitting on a shelf it has my attention and gets some clear ???Question mark markings to alert me to keep an eye on the cell .

For me it's sort of first in first out ..The bad being replaced by the good .Better cells replacing more questionable ones ..

I'm like comfeychair or Ubehebe..Almost exclusively stocked up with new unused OEM laptop pulls /all brand names .

Anything used is from older stuff I've gotten from recycling bins or recycled drill packs for Lmrs

i wouldn't try to drain it ..i'd bag it and tag it and make it disappear //Th e nice thing about laptop pulls is throwing the bad ones away feels like the exact right thing to do ...and gives you a reason to go look for more packs .

It holds voltage fine and except for the times it gets hot it charges to full voltage the charger can do, i tested all of them when i found the pack and a few weeks later none dropped more then 0.02V if i am remembering right, there was no single worst cell.

recycle the others from that pack too.
sanyo’s that have been overdischarged tend to do this.not worth the risk.

I’m not going to recycle the others yet, they were a laptop pack so hard to imagine them becoming over discharged, the computer and battery circuitry would have prevented that. If any of the others heat up like this one did then i will recycle them one by one instead of continuing to use them.

How do you know sanyos do this when over discharged?

Come on Bort. I hate to say it but I think you’re just trolling for friendly conversation and hoping someone will respond. If not, then you most certainly are aptly named. Your pattern is systemic and more then obvious: http://budgetlightforum.com/user/3888/cmf

Can you please stop this??

Huh, am i posting unreasonable questions or something?

I suppose i could ask on other forums, this is just the one i frequent and i post non flashlight stuff in Off Topic, so what am i doing that i should not be?