1989 cadillac alenta, 59,000 miles, had the key on with the radio playing, after about 30 minutes entire electrical system went dead. put a battery charge on the post under the hood and still dead.
Hmm, I’d check all connections to the battery…you can bring the battery to Autozone, or some other auto parts place, and have the battery load tested…it could have a bad cell or two, and won’t hold a charge.
Disconnect the negative battery cable, and reconnect it…do you see any spark? tiny spark is okay, but a big spark means that there is a short. Check the fuses to be thorough.