If they are in fact energizer 2500's those are know to be just about the worst batteries there are. Combine that with the 15 minute "charger" (more liek a cooker" that comes with them, they usually don't live past 50 cycles.
If your going to rely on rechargeables then get a decent charger and decent batteries. A charger that charges based on current not time if what you want to look for.