Pull the batteries, charge them up & take to a parts store to have "Load Tested". Make sure the cells are topped off with distilled water as well.
We have two group 27's in our 14' Thor class-C, they'll last a 3day weekend in the summer with fridge & water heater on gas. They'll only last an 8-10hr night when colder and furnace is used.
With just the basics on like smoke & propane detector, fridge computer, TV or radio & a light or two you'll be in the 9-13 a/hr range. On only 1 battery you'll only have.....
Group 24 = 6ish hours
Group 27 = 8ish hours
Group 29/31 = 9-10 hrs
Multiple that by the number of batteries you have. This assumes batteries are at a full state of charge, rarely are, especially with many OEM installed charger/converters. Add in extra devices like phones, laptops, more lights & water pump usage and it doesn't take long to see standard 12v's don't last long.....
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