One of the cells are low. you may have the cut off voltage to low or ran it too long. Your charger have a balancing you can check which cells is low. Set charger for nimh batteries set voltage .05v, watch balancing voltage the low cell reads 2.8-3,0v. reset your charger for lipo. charger will move to charge mode. When to charge lipo in nimh you got to babysit, do it manually stop charging every 30 seconds. until an average of # of cell 3.0v. Error on charger lipo wont charger until average of cell is 3v.

Good luck!!