Recently Tesla had a network outage which caused a very small number of customers to be unable to authenticate payment at superchargers -- and thus be stranded unable to charge. Due to the larger outage, they could not put in a new credit card either. (The system lost their working cards, they did not have bad cards.)

While it seems only a few were affected, it shows the challenge of having anything critical depend on a network that might go down.

I provide more details at Tesla’s Network Goes Out And Shows A Design Flaw