Jump started with no issues; all electric power returned as soon as cables were connected to another battery. I ran car for 90 min, then shut off; restarted with no issues. Four hours later, no power again: everything black. Next step?
Puzzling: the problem went away on Thursday: started up first time and ran all day; Friday morning was a repeat of Tuesday: starter clicked ONCE, and everything died before it turned over; it now STAYS dead with the car connected to another battery, so I cannot jump start it. should I remove the battery and test that separately?