I bought 4 Energizer AA 2500mAh Ni-MH cells that came with a simple charger. The charger is made for charging discharged 2500mAh cells and just has a timer (8 hours) to stop charging. If charged cells are charged then the timer over-charges them for 8 hours and they get very hot. When I charge 600mAh Ni-Cad cells then in 3 hours they are very hot.