So i left the country for over two months... and when i came back my new oddassy 1500 battery had competently drained... i charged it up, and drove the car around... it seemed fine, but if i play my music for 5-10 mins with the car off, the battery goes down to 10.5 volts and doesnt go back up, and its stuck at 11 volts turned off... is it pretty much dead or what? the battery is a dry cell btw and still under warranty.