true - sometimes you get one single bad cell in a 2S, 3S or 4S pack..and you have to buy a new pack...unless..you can identify which one of the cell in a pack that is faulty and replace that cell alone...this also if you can find identical cell specs as replacement, not to mention the danger that comes with it in taking the lipo apart.....best to use 2S x n or 3S x n as the smallest denominator if possible/can(battery tray).