Yeah, this happened to me yesterday. Woke up, car was dead. 80% charge in the main battery, but the 12V battery was only pushing 5V, so the main computer couldn't even wake up to unlock the car. Had to "jump" it with an external 12V power source. Funny thing was that this is the first time it has happened to me and it was in front of this guy's house:
Car died over night…. Apparently Taycans have the exact same crappy problem. Yay software. Apparently Teslas also suffer from this sometimes as well. The e-tron is apparently the easiest to recover because popping the hood is mechanical. I now have one of these in my frunk:
https://www.amazon.com/NOCO-GB70-Ul...l+12v+car+battery+pack&qid=1616514189&sr=8-19. It seems that you only need to supply external 12V power long enough to boot the main computer and turn on the car, which immediately discovers that its own 12V battery is depleted and starts charging it from the main battery. I really do NOT want to get good at fixing this problem.