We dry camp all the time in our coach with Residential Fridge. Ours is a the 18F Samsung, and draws 1.1A, so not a heavy electric user. (With ice maker off.)
Can could get better answers, if you could share the type and size of the two batteries involved? Does this coach also come with a Solar Panel system of any type (Many new coaches have Solar Panel systems installed as an option.)
We have upgraded our battery bank to X's 4 Lifeline AGM L16's for 800AH battery bank. Added a 1200W 48V solar panel system. So depending upon location, time of year, weather and other shading influences, we can go for days and days without needing to run the generator. Or, if in shade or snow covered panels, end up running the generator too:)!
More info on your specifics, would help in more constructive input:)!
Best,
Smitty