This happen to me too, thought it was a bug. But I replaced the battery that has 29% health left with 100% one and it worked again.

If you have the vehicle parked near a building during the outage it will cut off the power and water usage inside the rv make sure to have a ham radio and drive away fro mthe city when the power and water is going out should be fine

RV Interiors are just a room on the edge of the map. Outside that room is a generator. That's why after years of use it can cause a fire and burn your entire interior. But this isn't too common as it would have to spread 15 tiles or so. Let's just pray it happens during a rain and RNG is merciful.

You can use Debug to walk through the wall and fill up the gennie. On my server it lasts 600 days with the fuel it has, but we have the generators set to really low fuel consumption. It only uses 30% of the default amount.

If we power a minifridge in there it goes down to 90 days.

By the way, semi trailers don't even have a battery to replace. There you Definitely have to just use debug to get to the generator. In 'normal' vehicles with a generator, battery and interior I have never swapped the battery out and checked the generator time. Maybe somehow generator fuel level is linked to battery level? It's weird.