WRONG! So in their wonderful cheapness, the big power batteries that drive the car WILL NOT “start” the car sadly. And there is no “jumper” to even use all that power if the 12 volt battery goes dead.
The Prius, like a regular car, uses the 12 volt battery to start everything. So having a fully charged drive system can still result in a dead car if the 12 volt battery is dead (if you left the dome light on over night for example.)
That said, getting your Prius to “ready” state takes a lot less power than a normal car IF the drive batteries have sufficient charge. I have “started” my Prius with a household charge on a dead 12V batter in just a few minutes; just enough charge to get all the electronics to turn on and get the car to ready. Seems once the drive system is on, the engine had no trouble starting. Perhaps there IS a 12V charging system once the car is on? Not sure.
Lstly, given the stupid location of the 12V battery on a Prius (behind a kick panel in the hatch section, which you cannot open without power!!!), this is a LOT easier than jumper cables.