Expectation of heater overnight

How are the batteries being recharged?

MFL wrote:
Newer batteries, implies more than one, which should take you through a restful 40 degree night, without worry of charge.

Jerry

I have 1, 27 deep cycle and have not had a problem with 30 degree nights running my furnace at 70 degrees. With 2 batteries you shouldn't have any problems.
Brian

Can't speak to how quickly the batteries will drain, but I agree with another post.....an extra blanket or two, some warm PJ's, and you should be comfortable without using the heat at all.

Unless you absolutely need to heat the interior, (you said 40's, so no freezing pipes) just layer up and crank the heat up first thing in the morning. Those heaters work pretty well to take the chill off quickly.

I've been told that heaters pull a lot of juice. At 40 degrees it will probably run frequently but probably won't exhaust your batteries. For me, the heater is noisey and wakes me up everytime it turns on so I'd rather just use an extra blanket then kick on the heater when we wake up.
I'm surprised they haven't set up timers on thermostats. That way you could set it to come on for say 15 minutes or so every other hour or so. My FW warms up fast and stays comfortable for a long time with the windows shut.

Agreed if the OP has 2 good batteries. The furnace should survive overnight without issue

Newer batteries, implies more than one, which should take you through a restful 40 degree night, without worry of charge.

Jerry

kerrlakeRoo asks a good question, I'll add how old is the battery or batteries?

What size battery, and how many?
A furnace fan will draw a single battery down fairly quickly.
Standard RV furnace draws about 7 or 8 amps for the fan when running.