I think the problem is in the "shifter". My brother, who owned the car my Mom has, said that he had to have some corroded / intermittent contacts in the "shifter" fixed. Because, it is an electronic control - there is no mechanical linkage to the "transmission"; which is a one-speed reduction gear.
This also can prevent the car from being charged, because it doesn't "know" it is in Park.
The dealer charged my Mom about $250 to fix the issue in the "shifter". It is not the 12v battery, in our case.