? about boondocking with furnace

Our two T-105 6 volt batteries in series ran down one cold night before morning as the furnace kept cycling on and off frequently, annoyingly so. I never tried to adjust the thermostat to change the on/off frequency. The condition of the batteries and the level of charge at the start of the night time heating period will affect how long they can power the furnace blower. The resistance losses from 12volt wiring and cleanliness of the connectors at the battery terminals can also have affect power from the battery(s). These factors can make calculations of battery power duration to discharge misleading. It would be a good idea to measure actual current draw with furnace running It helps to insulate windows and windshields etc., to minimize heat loss but RV's are not well insulated for either cold or hot weather. Running the RV generator to re-charge the house battery(s) will probably take hours of generator run time and bring complaints from other campers. Using a fast automotive battery charger while running the RV generator might be faster but harder on battery life.