Battery "life" is measured in reserve capacity, which is how long in minutes it takes a fully charged battery to reach 50% state of charge (about 12.2 volts) at a discharge rate of 25 amp-hours. A pair of typical flooded lead acid 6v golf car batteies have about 400 minutes RC, so less than 7 hours.
I inspected a Travel Supreme coach last year that was all electric; oven, stove, fridge. The heat was Aqua-Hot. It had 8-6V batteries, 2-2000 watt inverters and a 12.5kw generator. I'll bet that it would not go the night with the heat on.