the mobo may only be a few months old but there is no telling when the battery was made. Batteries drain down slowly in storage, which is why they put a use by date on the packaging. Also it could just be a bad battery
for $20.00 from Walmart you can get a Belkin transmitter that plugs into the line out of your pc and set the radio in the car to the appropriate station it plays through the car wirlessly I use one with a portable mp3 player, 10 hrs of music, one cd