Is a LIPO with one dead cell usable?
 

Bought a 4-cell lipo from a fellow RC tech user and one of the cells is at 0V. The dead cell is on the end and swollen. A lipo cell checker confirms three cells at 4V and the last at 0V. Voltage at the battery plug is at 12V. Assumed that is is not safe to use since I received it that way for over two months now and had not used it. I came across a sale post here on the forum that the user is using a lipo in this condition for over 20 cycles. So I'd like to hear some opinions on this subject. Thanks

I wouldn't use it the way it is - I'd be worried the puffed cell would go ahead and vent or whatever and damage everything around it. Discharging it with the puffed cell attahced or charging it that way is asking for trouble.

If you're comfortable doing it, take the pac apart and make it a 3S pack and re-shrink it.

That is a dangerous situation waiting to unfold.

If your intentions are to use the battery, remove the dead cell and use the good ones as an actual 3 cell instead.