Maybe this belongs in the stupid question thread, but where is the safe place to dispose of cells?
Most of the vent and flame thing with li-ion is exaggerated gossip, I think. If you read Intertek's guide to the UN requirements for lithium battery testing prior to transportation, in page 9 you can see the overcharge test for single li-ion cells implies “2x voltage and current” for 24 hours, with a “no disassembly or fire within 7 days of test” pass criteria. Serious benchmark! 
And you know… well, everything's possible I believe. ;-)
Cheers ^:)
Oh, I agree that many people are far too paranoid about lithium-ion cells. But, I wouldn’t keep a cell that stays hot when it’s not being used. That is trouble.
Stick it in a metal can and let it cool down. Line the can with some plastic so it doesn’t short. When it reads close to 0 volts, throw it out or recycle it. I assume it’s an internal short, so it should discharge by itself over a few hours or days.
I wouldn’t trust Nitecore to have used only cells from quality brands. I wouldn’t trust shady chinese cell makers (there are tons of them) to produce anything that passes regulated tests.
The temperature OP describes shows either the cell or the circuit is damaged (or both). Not necessarily will this lead to a thermal rundown, but it very much increases the risk. As this produces at least poisonous fumes and fire, who wants to use this cell anymore except somebody who doesn’t care about himself or others?
And the voltage clearly is way off, so using the cell might damage anything you put it into. Why bother.
only way i can see that cell reading 9.xx v is on a harbor freight meter with a low battery.
they can be wildly inaccurate when the battery is low.
the heat is damage to the charger/protection board.
i would take it off and convert it to unprotected.
cell is likely fine.
Update: Over the course of the few hours, voltage has gone down and now reads 9.68.
Good to know that it’s exaggerated. Made me a bit paranoid that it would blow up in my face any moment. lol.
I’ll consider this. It would seem like a waste to just throw it out willy-nilly.
All my funky cells go to the local hazardous material waste site. They take old electronics, engine oil, paint, etc.
I would be concerned about how it got to over 4.2v, that makes me think there is a charging issue.
No I would not keep it, at least as is, maybe if the protection circuit was removed.
If those measured voltages are right (9.96V, then 9.68V after a few hours means damaged cell), such cell should be disposed. I've seen cheap 4.2V cells die just by overcharging them up to ≈4.35V. It's not worth taking a risk in this case.
Cheers ^:)
for reference comparison, Samsung 30Q specs PDF indicates it undergoes factory stress tests by overcharging to 20v:
“Level 1”: battery damaged (leaks), but doesn’t explode…
It’s toast and to cheap to replace to risk burning your house down. Dispose of the cell and replace it.
Toss it in a bucket of saltwater solution, and set it outside for a couple days. It should be good and dead by then.
If the instruments you’re measuring these batteries with consistently measure other known voltages accurately; please do not sleep in a residence with this battery in it.
Easy enough to read less voltage from a battery, requires a specific circuit to put out a reading at 2X what you’re expecting.
There may be special circumstances but if the battery was “quite a bit hot as I got it out of my MH20, which btw was off and not in use for hours” there’s a problem.
Don’t risk it. I wouldn’t trust a cell like this anymore.
If you want a unprotected cell just buy one they are pretty cheap.
I’m not sure that test indicates the cell is charged up to 20v. It may just be that they use a 20v load on it in order to force current through it to overcharge it. Can a lithium-ion cell even have a resting voltage more than about 5v?
This.
a $10 cell is hardly worth the risk
Batteries Plus, or anyplace like that, will take the discard cells.
DO NOT toss it in the saltwater solution like Robert B said! BAD ADVICE!
I’d remove the wrapper and cut the protection circuit, see if it stays a problem with the protection circuit disabled. If it seems fine then I’d remove the protection stuff and re-wrap it, keep an eye on it in use in a regular flashlight and see how it goes.
If the resting voltage is 9.68 volts like the op stated above what use is it. If he sticks it in a flashlight it could fry his driver or give to much current from the higher voltage and go “POOF”.
I=V/R
His over twice the normal voltage. You might try removing the PCB but I don’t think the circuit can boost twice the voltage. Far as I know it’s just a simple controlled FET switch.
Single cell XHP70 light? 