You didn't mention if you are a "do-it-yourselfer"... If it has a dead battery now, won't crank, remove the battery and charge, make sure you have the radio code of course. Start engine, hopefully, and put a digital volt meter across the battery with the engine idling. You should have 13.5 to 15.5 volts. While watching the volt meter, start to turn on the accessories, one at a time and watch the V.M. If the voltage reg. and alternator are healthy, it will adjust to the loading and maintain this reading. The minimum you want to see is 13v.
BTW, you can get digital V.O.M.'s at Radio Shack starting at $10, and you can do a lot of trouble shooting with one, if you want to of course.
If your charging system is working rt. then it may simply be a sign of a bad battery. Tom