Replying to Physics help

alright, I am guessing that only college level physics folks will know how to do this, but if any of you think you can do it, give it a whirl. Basically, I just need to find out how much energy is lost in a battery, then the rest of the question is as easy as plugging that into E=mc^2. so here is the problem

A certain 1.5-V battery (whose original mass is .425 kg) has a capacity of 4.5 Ah. About how much lighter is the battery when it is discharged than when it is full [Hint: It has the same number of electrons when "discharged" as it does when it is full]

so, based on that hint, like I said, it should be as simple as finding the energy released in that battery from when it is full to when it is dead, and plugging that into E=mc^2, I can find how much mass was turned into energy.