HELP please. I bought a 91 jimmy S15 it has a short circuit or a power drain . I charged the battery to 14 volts. 2 hours later it was 8 volts. it is a new napa battery . i am an electrician have meters etc.and do know how to use them. but this car is getting to me. while connected in car the battery will not fully charge.only to 12.3 volts after 3 hours of 6 amp charge. Has anyone else had this happen?