Kinda backwards question, should be: hong long can you run on batteries before you have to turn the genny on?
Unless we HAVE TO have A/C, we run our 8k onan QD for an hour at breakfast time, and an hour at dinnertime.
The rest of the time our standard battery bank and factory 2k inverster take care of everything.
The only thing I don't like about nascar infield camping is all those towable owners who seem to think they must run thier 6500 watt open frame champions 24/7!
Even a cpac will run all night on a 400watt radio shack inverter and a good battery.