You simply keep the car "on" in either EV or HV mode and the power for the 120v inverter is pulled from the DC to DC converter which continuously keeps the battery charged. I did this with my Prius years ago so the car is my V2H (vehicle to home) power supply to keep my fridge and few lights on in a power outage. You do need to use heavy gauge wire to connect the battery to the inverter. The car's 12v accessory plug can't supply the required amperage. With this system the ICE only cycles on 4-5 times per hour for a few minutes each time. The wire gauge you need to use will be function of the inverter capacity. Mine is 1000w continuous/2000w surge and I used 1/0 gauge with an in-line 80 amp fuse. That's a bit conservative but better safe than sorry. There is a lot of information on doing this on the Prius Chat forum. Good luck.Ah yeah that makes sense. What gauge wire Is used to connect directly to the battery? So many choices on Amazon, if you are happy with what you got, which one is it?
Also, if the 12V battery is an AGM I guess that would work better this way than a typical starting battery, but what would I have to do to keep the 12V charged while using the inverter? Sounds like something that could be a good solution... Thanks!