I have a 2015 ACE unit with (I assume) 2 original Marine Master coach batteries. I am not the original owner. If I were to use them at night, not running the generator, to operate the furnace should they last the night, assuming they are properly charged?
They should last posted previously but if they are the original batteries, they are now approaching ~5 years old. Depending on the number of charge / discharge cycles and how deeply discharged they have been over time, you might be needing new batteries at some point in the not too distant future.