Sorry but that lipo will be dead, from memory 2.8v per cell is minimum capacity I have my cut off set at 3v per cell,
So 6x2.8v 16.8v .this is not always dangerous but it will have damaged the battery capacity and current draw. The chargers won't charge below set voltage points because if you charge the lipo it is likely it will puff and be potential dangerous, my advice bin it safely and get a cutoff unit or a buzzer alarm at least whilst testing,