Entire Prius computer system
Entire Prius computer system is operated by the 12v battery. If there is a problem in the 12v system, it cripples the entire car.
Most "ordinary" cars notice a 12v battery problem because the car starter puts a FANTASTIC load on the 12v battery when starting.
so when the 12v battery starts to go bad, the car starts slowly or not at all.
Prius does not use 12v starter, car ICE engine starts on the 200v propulsion battery.
Several prevous posts by people because either the 12v battery went bad, or the 12v charging system went bad, and the whole car died.