Why does my Fiero keep killing batteries?

If it is a draw, I cant tell you were it is, but to check for a draw unhook the negative battery cable and take a volt meter from the cable, to the negative post on battery, you should not see more than 2 volts.

To add to to Rowefasts reply if you do have a draw, you need to pull one fuse at a time then check meter to see if the draw goes away, this isolates what circuit you need to look at, This is called the parasitic draw test, type that in and go to utube and watch the vid if your not too sure. Eric the car guy has i simple and good video you should watch

Good analysis there StevenBoussey.

also ..could be the alt..over charging...frying the battery!