The energy changes from stored energy to chemical energy when the energy goes through the wire in to the thing you are powering and out the other wire back into the battery it is then called chemical energy this is what makes the battery go dead after all the stored energys gone. When you charge a battery it puts more stored energy in your battery then your battery will be able to be used again if your battery is rechargeable. if your battery is not rechargeable your battery is know useless. When you use a battery it goes from stored enegy in the battery to chemical energy.