12 volt battery and heater question

[rhodesaz]

We have a 2013 Itasca Sunstar and towing a 2009 PolarisRazr. We are getting ready to go (next week) to Southwest Utah - Bryce, Zion, Kanab and surrounding areas. I saw that the weather will be cold (near freezing) at night and nice during the day. We will be dry docking several times over the next month.
My question is: how long will my two 12 volt batteries (dated Oct 2017) last using the propane furnace? I know the batteries will run the fan and sensors, but how long will they last with out a charge from the generator? We've never boon-docked before. We plan (hope) to have electricity every two or three days. Then boon-dock for a couple of days. Electric for a day or two and then boon-dock for a couple of days, etc, etc...
I also know the more lights I run at night, will/should decrease the life of the batteries.
We do not have or plan to have SOLAR before we leave.
Thanks in advance for your input!!

[vanmark]

You should be able to run the furnace fan as needed thru the night with the average size batteries. You will need to run the generator for about two hours first thing in the morning and about two to three hours of the evening before going to bed. This would be a general guess, based on a 36' motor home we used to have with two batteries. The furnace fan takes a lot of power. Run the generator as late as you can and as early as you can and you should be ok.

[rhodesaz]

Just a follow-up to my earlier question. We boon-docked over night with NO utilities. The display panel showed the batteries at full when we went to bed. In the morning I noticed the display panel showed the batteries at 2/3 full. I had the heater/furnace set to 60 degrees. It was 34 degrees at 6 am. So, the two 12 volt deep cycle batteries lasted all night running the heater/furnace (plus all the sensors) with no problems. Of course I fired up the generator first thing to make coffee and re-charge the batteries. It only took 15 minutes until the panel showed the batteries fully charged.