Camper battery compartment project

[Richburgers]

Hi there, I’m working on a camper project that has to do with heating a battery compartment to allow Lithium batteries to charge properly through the winter. Inside this compartment there is a small heater fan that will be controlled by a digital thermostat to keep the interior temperature around 45 degrees. Exterior temp is 0f. The heater fan is 12v, 100 watts, and generates approximately 340 BTUs. The dimensions of the box will be 2x1x1.5, with an approximate R value of 4. Based on that insulation, I THINK my heat loss is approximately 8 BTUs an hour but y’all might wanna check my math. What I’m hoping to find out is how frequently the heater will have to turn on and off per hour and how much power (amps) this will use in a 24 hour period based on a 12v system.
I really have no idea what type of math this would be so I figured this was the best place for it. If you need any more details that I may have left out I can try to get them to you. Thanks I’m advance!

 

[anon_hedgepig]

You're missing units on your box dimensions. Feet? meters?

Also, would be nice to give consistent units (SI units?)

There really isn't any point in trying to figure out how frequently the heater will turn on and off, since you can just use steady state analysis (as you probably have) to determine the heat flux given that you know your interior should be 45 degrees and your exterior is 0 degrees.

That being said, it's hard to tell what your loss figures are actually gonna be because you don't have static conditions (consider wind, exterior temperature changes....)

Also, charging batteries doesn't occur with 100% efficiency, so that waste heat will also heat the compartment.

Basically, this question isn't really "solvable". Needs more info.