Welcome to just answer.com. I'm here to help you and your 100% satisfaction is my goal. If the batteries going dead in the batteries knew very likely you have something that's drawing current when the car is turned off .using a meter Install the ammeter with the Black lead on the battery terminal and the Red lead on the battery negative cable. It may be necessary to wait for up to 1 hour to take a reading. Waiting allows all of the computers to go to sleep,,, if you detect a battery drain on the meter start by disconnecting the radio this is the most common trouble spot

The radio does not need to be altered to go bad and become faulty it can become faulty all by itself. If the alternator caught on fire most likely is overcharging at some point, or it has faulty connections on the wires causing excess heat. Make sure the wire connectors are all clean and tight. Then make sure the engine, the body, and the alternator are all properly grounded. These are the most common causes to look for

You may want to it and an additional ground wire to the case of the alternator just to be sure