This is correct, and actually stated in the owners manual. You should NOT use the vehicle in ACC mode for anything more than just a minute, especially NOT using the radio. It needs to be left with the vehicle started, in the RUN position, and let the car go to Auto Stop and Start. This will charge the battery as it should be charged when needed, and will stop the vehicle when not needed.

The manual mentions this specifically, as there are too many electronics in the vehicle that draw too much power. You can easily kill the battery in less than 10 minutes with the radio running in ACC mode without being in the "run" position.

 

Hillbilly_Hybrid is right. The engine is started using the 300V battery. The 12V is basically for control. Notice the headlights don't dim. Because they are on the 12V side. No amount of current at the 12V level will help to start it if the 300V battery is low. The 12V system is charged off of the 300V system. This is why they limit the 12V accessory current. Be careful when using the old fashioned "jump" starters. They ramp up the voltage to attempt to deliver enough current for a conventional starter. You may end up with a BBQ flavored ECU.

 

I am a mech, if throw a meter on and you turn the key over while looking at the meter. If it drops below 10 v. Low battery, it will not start. Need at least 11 to 12 vdc to start. Trickle charger will help to keep it charge. The only problem is if u keep jumping it, it does degrade the battery. I recommend a dry cell battery, they cost more. But no matter how many times it goes dead. It can be recharge or jump and don't degrade. I have one on my boat. So they will go dead in the winter. I charge it up and ready to go.