Sid, the last two batteries in my El Camino shorted out just like that. I could not even jump start the car. The battery was fine one minute and just dead the next.
My brother has a 1974 VW camper that he goes on many camping trips in. He started carrying a separate battery with him. He can use one battery to run fans or lights without starting the Van and have a backup if needed. Of course it is possible to push start a VW.
You were lucky you had cell coverage.