It's worse than that: it requires the old school lead acid 12v battery to be charged, so even if the car's battery is full, it doesn't matter if that old car battery has failed
That's not unique to Tesla EVs, but it being required to open the doors may be (the 12v lead acid runs the general vehicle electronics rather than down converting the 400v or 800v main battery... I don't understand that decision, but I'm no electronics expert so there may be really good reasons for it...)