Root [AT&T] Sudden inexplicable battery drain and switch-off

[QueenMabel]

I installed Cyanogenmod 10.2 on my AT&T Samsung Galaxy S3 a few days ago. Twice now I've had my phone suddenly switch off, and when I turn it back on, the battery history shows an instantaneous drop of 30% or so at the point where it switched off. And I mean literally instantaneous. (I can't post screenshots as a new user, but will do so as soon as I get the rights to.) No particular app is showing up as abnormal. Anyone else had something similar happen?

 

[Rukbat]

Sounds like a dendrite in one cell. That's a short that grows (like a crystal), punches through the membrane, shorts the battery and gets broken by the current. But it drops the battery voltage enough to turn the phone off.

It's a warranty issue (there was dirt in the clean room when the cell was being manufactured, so it's definitely a manufacturing defect), but a) try to convince the phone manufacturer, unless you happen to be in the Lithium Ion battery business (as a design engineer) and b) good replacement batteries on Amazon are cheaper than waiting on hold for 5 minutes with "customer disservice". If you deal with a really great shop, they might replace the battery for you, though - it depends on their relationship with their distributor.

(There's no way to "repair" it unless you have a clean room, because the air in your room is a lot dirtier than what got into the cell.)