TTurboVoltage

I have a 1995 SC, it went dead on me once so I charged it, then I parked it in a garage for a week or two the radio still worked after I charged it up and parked it, I got it out of the garage to do some slight maintenance on it and the radio still worked after we got it out, then we put it back in the garage, only to get it out Friday and the battery was dead, we jumped the car and then put it on a charger, the radio worked for a second or two just to go back to silence. I parked it and put a battery tender on it over the weekend, I checked it today, and it turns on and shows radio stations/playing tapes but there is no sound. What do I do?