I was out flying 4S on my quad and during flight and my battery alarm disconnected. When I landed I checked the voltage again and it was at 12.0v (3.05 - 2.72 - 3.07 - 3.16) . As it's a pretty new battery with only a few flights on it I didn't want to waste £20 on it so I'm currently charging it really slowly at 9V 0.3A and it is going up slowly and is now at 12.2v. Am I doing it right and is there any hope for it (without burning my house down)?

It will be fine but not the best practice, charge and store properly.

Originally Posted by rcflip

It will be fine but not the best practice, charge and store properly.

It seems to have stopped charging at about 12.2v (3.09 - 2.79 - 3.10 - 3.22) and doesn't want to go up. It's been at that exact voltage for like 15 mins now...

Start the charge again, I have run batts down to 2.9, 2,9,2.9,2.8 and they still go like the clappers, look for obvious signs of puffiness, heat, etc. If in doubt toss it.

Originally Posted by jonnyflyboy

Start the charge again, I have run batts down to 2.9, 2,9,2.9,2.8 and they still go like the clappers, look for obvious signs of puffiness, heat, etc. If in doubt toss it.

Had to stop charging as it refused to charge at all. Cell 2 somehow dropped to 2.25v. Pretty much dead now, oh well.

Charge on NiXX setting at low current (~.5C) for about 5 minutes with balance disconnected from charger and then terminate charge, switch charger to 'lipoly balance charge', connect balance tap, and initiate a 4S lipoly balance charge. Problem solved.

I've accidentally run packs down lower than that once or twice and they recovered. The key is to charge them back up quickly, don't wait around.

Originally Posted by mrforsyth

Charge on NiXX setting at low current (~.5C) for about 5 minutes with balance disconnected from charger and then terminate charge, switch charger to 'lipoly balance charge', connect balance tap, and initiate a 4S lipoly balance charge. Problem solved.

Yes, good option.

If the cell voltage dropped while on charge, it is probably because it has an internal short. You try to put more voltage on it, it could burst in to flames. It might just do that anyway, on its own. I would discharge the pack completely, outside, attached to a 12V car lamp, and then dispose.

Originally Posted by rocketsled666

If the cell voltage dropped while on charge, it is probably because it has an internal short. You try to put more voltage on it, it could burst in to flames. It might just do that anyway, on its own. I would discharge the pack completely, outside, attached to a 12V car lamp, and then dispose.

It's naturally kept dropping as well. Cell 2 is down to like 1.28v, the other cells are at 2.6-3.1v. It was also very hot when just sitting. Internal short on cell 2?? Good thing I left it below a smoke alarm in a sand bucket overnight. I hooked it up to my quad and let the motors run until the battery was down to 4v and that seems to have finished it. Well, that was a slightly costly lesson . Thanks for the advice.

Originally Posted by opticulex

It's naturally kept dropping as well.
It was also very hot when just sitting.
Internal short on cell 2??

Yes. This is absolutely the sign of an internal short. "Hot while sitting" means the same as "ticking time bomb". You're lucky the short was "high impedance" or the cell may have gotten hot enough to ignite.

4V isn't it. A discharge LiPo will read near zero V. There is a minimum below which your quad's ESCs won't run, though. That's why you want to use something like a filament light to run the pack down. That will get it to zero Volts in 24 hours. Then you can throw it in the trash. Lithium batteries are safe for landfills and fully discharged they are not a fire hazard.

A lipo pack with less than 30% capacity left in it is reported not to be a fire hazard. It will just get very hot if it does go into thermal run-away without any flames.
Looks like that is what could have happened to your pack.

It is possible that it might come back. Instead of trying to charge it at very low voltage it is better to charge it as a 4S but at very low current like 50 to 100 ma.

If it does not have a dead cell then your chances are pretty good but keep a very close eye on it. If it gets hot or, if it will not charge beyond some voltage that is less than fully charged then get rid of it.

Rise from the dead? I doubt it.
He has already discharged it to less than 1V/cell.

He has done what you suggested at a charge rate 0f 0.3A. See posts #3 and #5.



(I know it's chore to read the whole thread sometimes....LOL)

If it gets over-discharged it will usually come back. If it spontaneously self-discharges then no way, it's done for. Trying to recover a cell that is self discharging is begging for a fire.