I, too, am surprised that Tesla hasn't licked this problem. I believe the last time this happened to a number of owners, it was traced to a bad batch of 12V batteries. It's essentially a motorcycle wet cell battery. I'm surprised Tesla didn't go with something a little more rubust, like a gel cell. Since this 12V battery powers the relay that allows the main battery to connect to the car, you're dead in the water if that 12V battery goes flat, even if the main pack has some juice left. I believe the 12V battery also powers the locking solenoid on the charge port. There's a lot riding on that one little 12V wet cell.