Disconnect the battery and charge for 24 hrs check the voltage after 3 days anything below 13 v is suspect 12.8 is a definite change battery. If the battery is not losing charge reconnect and put a meter in line set on milliamperes see what the leak is, anything more than a few milliamps you have a leakage. Disconnect all the auxiliary units like alternator, starter etc one at a time until you isolate the offending component. Oh and don't forget to check alternator output should be about 14.2 at 2000 revs.
