I assume you know you can change the settings for the automatic start on the generator. After adjusting mine I can go 7 hours on 2-6 volt batteries. I plan to add 2 more batteries but will wait until I need to replace the 2 I have so I can have 4 of the same age. In the mean time I don't use the generator auto start for overnight. I use the generator in the evening for a few hours to top off the batteries and shut it off at 10:00. At 7:00am the fridge is still below 40 degrees.
I do use the auto start but only in the daytime if I plan to be gone.
Hope this helps.