Yeah the ioniq/(hyundai kia etc.) is the only hybrid I was aware of with a 12V recharge button like that, that link certainly shows why it can have that.
I was under the impression the prius didn't use the 12v to start the car per se, and there was no starter motor, only MG1 and MG2, where MG1 was doing duty as the starter. I had a motorcycle that did a similar thing, the alternator was the starter.
My understanding is you need it, because the 12v is initially used to run the system computer, and close the hybrid battery relay. Once that happens, the hybrid battery energizes MG1 to start the engine.
I was under the impression the prius didn't use the 12v to start the car per se, and there was no starter motor, only MG1 and MG2, where MG1 was doing duty as the starter. I had a motorcycle that did a similar thing, the alternator was the starter.
My understanding is you need it, because the 12v is initially used to run the system computer, and close the hybrid battery relay. Once that happens, the hybrid battery energizes MG1 to start the engine.