battery died on 1990 Chevrolet Lumina

battery died when car is off something is draining the battery

1 answer
do you have a tereo or amp that is not being turned off when the key goes off
you could also have a bad voltage regulator charging the battery when running but running the bat voltage backwards thru the diodes in the alt regulator to ground
check after the car is cold and see if the alt is still warm,indicating a shorted voltage regulator/alternator