No one here can tell you how long you can go because no one knows what equipment you have, and there's no way to know how much it will be run because it literally depends on the weather. It could be one night, it could be a week.
If you want to know how to estimate it, you measure what all your electrical loads are and compare that to your battery capacity. As an example, I recall my heater draws 7 amps when it's running. Around 30F outside, set for 68 inside it runs for a total of 20 minutes every hour. So that's 7amps for 1/3 of an hour, 2.33Ah. Times say, 8 hours overnight is 18.6Ah. I know my batteries are a solid 200+Ah so roughly speaking, I could run my heater 10 nights. Now, throw in lights, refrigerator, TV, water pump and everything else you run and your capacity is used quicker. But experience (and a few driveway campouts) has shown me that I can easily go for days running whatever I want and still not kill the batteries dead. I end up charging them just because I should, not because I have to. Until you get an idea for not only what your devices draw and what your batteries will hold up to under YOUR conditions, you'll just have to watch and see as you go. Hopefully you have some kind of battery monitor to see where you're at and can see how quickly you're draining them, so you'll get an idea whether you'll make it through a night and not wake up to a cold dark RV.
Mark B.
Albuquerque, NM
;D
