car maintenance repair help diagnosis (Battery)?

You need to charge the battery with a portable battery charger, 12w volt @ 10 amps for a minimum of 6 hours and then have the battery tested. A bad diode in the alternator will cause your problem too. You only get a surface charge when one of the diodes is bad. If you have a volt meter, check the voltage across the battery terminals with thew motor off and then on. 12.3 to 12.7 is a normal voltage reading with the motor off. Start the car and you should have 13.7 to 14.6 volts. If you don't get at least 13.7 volts rev the motor to 2,000 rpm and check again. If you still don't have 13.7 volts minimum it's time for an alternator. I'd replace the battery too if the battery is more than 3 years old.

No why would it affect your battery if the power isn't on in your car once it's off... Sounds like you have a bad battery. I had the same problem so you know what I did? I got a new battery.

HowTo Recondition Batteries At Home : http://battery.findpolo.com/

it could be ! when your not going to be driving it for awhile unhook the battery and then see if it will start after you hook it back up ! it could be that the battery has a weak or dead cell in it too and going dead !