What would eventually happen to the battery as it degraded? Say a battery accidentally got into a box going into the attic, never to be seen again. Would a fire/explosion be inevitable? Is it predictably possible that nothing would ever happen (%wise)?
TIA
Coscar
I’m wondering that myself. I misplaced an UltraFire 504B a couple of years ago with a Panasonic18650 installed in it. I need to find it before the cell discharges several years from now.
It would self discharge until it becomes permanently damaged and unusable.
No it does not explode.
likely nothing will happen just sitting. I believe the danger comes when you try to charge it again. The charger will send pulses of higher voltage to try and wake the battery and the charger may not know it’s bad or may not care and keep trying to charge it. Cell warms up, bad things (may) happen.
If there not used they seem to be fine even after several years even at a very low voltage. So I don’t have a answer for you and doubt anyone else really knows either.
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Interesting reading on old cells left in a low voltage state. FYI - some 'new' Fujitsu laptop batteries
Interesting part starts about post #14 and continues on to the end.
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I do have some cheap trusfire cells that have sat for 6 years or more and they haven’t caught fire yet. I don’t use them anymore but it’s about time I either give them away or recycle them. 
Depending on on the chemistry and separator composition. Upon full discharge you might have copper dendrites form in a fully discharged state over time and upon charging you could possibly get a short. With the older lithium-cobalt chemistry, you could get venting with flame.
The problem is in the charging phase, but then it’s kind of too late.
Chris
Shorting a battery rarely results in fire or explosion, they just get very hot until they are discharged.
If the battery is already discharged, shorting it will do nothing.
What did I write that you don’t understand?
I think we can agree that, at least for our purposes, venting with flame and explosion are pretty much interchangeable, but no…li-ion chemistries aren’t classified as explosive mixtures by the ATF (>~21,000fps.)
Explosions do happen in sealed tubes like flashlights and E-cigs. I watched the local news yesterday and some guy was shopping for TVs and his E-cig popped and you could see everything on the security camera. Most people would describe what I saw as an ‘explosive’ event and he was burned badly.
Li-ion cells do get hot and vent with flame. Lithium-cobalt has an oxidizer, so it can even pop in a vacuum, or vent with flame in water, if the core temperature is hot enough.
The problem with copper dendrites is that they form and create the short, but since the cell is depleted there is no heat build up due to a lack of energy, so no real issue there.
As I previously said, the problem occurs when the cell is unwittingly charged back up as if it’s in good shape and as the energy is transferred back into the cell, heat builds up to the point of thermal runaway.
Haven’t you watched the news over the last 5 years with the hover boards burning houses down?
Most are mechanical shorts via shoddy workmanship, but some are just crappy batteries of dubious origin that could have been sitting discharged in a warehouse somewhere, for years.
That’s all thermal runaway.
Chris
they lose charge about 1% a month, eventually the volts drop to where a charger should not try to charge it (1.5V-1.0V) to avoid fire and explosion
what happens is, when very discharged for a long time, metal fingers form between + and -, causing an internal short that can get hot and ignite the cell if charging were attempted.
Why are you not posting the thousands upon thousands of videos showing li-ions venting with flame? Were not hover boards a problem a couple of years back? E-cigs currently? Samsung cell phones and Apple laptops?
What do you suppose causes that and what’s actually causing the fires?
Shorts can create heat and as the temperature rises, the cell can go into thermal runaway and in the case of the li-co the chemistry, venting with flame. Are you denying that li-ion cells, of any chemistry, do not have thermal runaway points?
It comes down to probability and they’re very safe, but to ignore the reams of evidence, that something does happen in an unfortunate situation, seems to be a form of ‘denial.’
Chris
Maybe you’re confusing li-ion with lipo.
Lipos explode much more easily.
As for cylindrical li-ion cells, take a look at tests people have done on youtube, either shorting the cells or overcharging them.
In almost all cases they won’t explode, they just heat up.
Obviously if you force 20 amps into one using a power supply instead of a regular charger then it will vent.
You sound like you’re very paranoid, and overestimating how often 18650s actually vent or explode.
If there is no more electrical power left in the cell, it will not explode.
Shorting an empty cell will not heat up the cell because if there is no more power, it can not heat up the cell.
Cells that are lying around somewhere do not cause fires, cells that are being charged (overcharged) or discharged with high currents are far more dangerous than empty cells in the attic.
If you try to charge a completely discharged cell, then there is a possibility that it can go wrong.
I guess we can agree to disagree.
I’m being pretty succinct and I’m carefully qualifying what I write.
LiFePO4 has a higher thermal runaway point than either lithium-manganese, or lithium-cobalt (which isn’t being used much, if at all, by the Big 5) so that’s not it, but yes, many of the hover boards aren’t using cylindrical cells in their battery packs. E-cigs are another matter.
Oh…and I have li-ion cells and chargers coming out of my ass, here, so that’s not it.
Anyhow…
Chris
Even shoring a charged cell makes it heat up a lot, but even then rarely does it explode or vent.
Well I’m not saying that no cells will vent or explode, and I’m also not saying people shouldn’t be extremely careful when using lithium batteries.
I’m just pointing out that many people have recorded videos of shorting or overcharging cells, and many of those videos show the cell heating up a lot but not burning or exploding.
At what voltage is a 18650 considered completely discharged or to the point where it would be considered (by most) dangerous to re-charge?
I’m talking about you forgetting about it for 6-12 months and when you find it, you’re close to zero volts.
There’s a time component, where the dendrites form, so if you charged up a cell right away, after depleting it, you wouldn’t have any big issues.
If it was a li-co and that did happen, I would be recycling it. Since li-co chemistries are rarer these days, it’s probably not much to worry about.
Chris
I just had a 26650 get bricked. Nothing. Dead. No OCV, no charging current.
How hot is considered dangerous when charging an unused 18650? Is it when its too hot to touch or just warm?