Have to jump to start. New battery & alternator is charging at 13.5 volts. on 1990 GMC Jimmy

After jumped & vehicle runs for about 15 minutes & is charging at 13.5 volts, it will start the rest of the day but when vehicle sits all night, have to jump start again. Help!

Asked by for the 1990 GMC Jimmy
Something is draining the battery overnight. Close all doors and make sure there is no interior lights left on. Check glove box light. Check under hood light. If all are off then take it to a shop that has the equipment and diagrams to diagnose a draw on the battery could be almost anything.