Power Output

I have chosen to hook my device up to a 6 volt light bulb although my final device will be used to charge batterys. The reason I went with a light bulb instead of the battery charger is simply because it cost far to much to buy a battery charger and pull it apart. So I have reasearched into solar powered battery chargers and found that to charge an AA battery you only need a small amount of voltage. So if i can make my device run a 6V light it should easily be able to charge 1-2 batterys at one time.