Had similar issue at 50 percent, voltage dropped suddenly to red figures upon gaining attitude, return to home was about to be initiated, but I cancelled it and managed to bring her back carefully. Battery life was at 98 percent and it had around 50 cycles. I later drained the battery down to 5 percent, recharged it and it has not happened again. Strange, as there was no indication that any of the cells was bad, voltage was quite similar across the cells and battery was pushed all the way in, I always check that before takeoff.