info is missing.

if the car running is only producing 12v what is the voltage with the key on, but engine not running? try this. start the car, measure the voltage at the battery. leave the key in the run position, and hit the stop lever on the motor. measure voltage again. what is it?
your meter is measuring DC voltage. your alternator could be putting out 30 or so AC voltage too... that would certainly boil a battery.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!