Batteries and heater for solar system?

I’m currently going through Will Prowse’s purchase list to build a 400 watt solar panel system for a pop up pickup camper. I have purchased everything but the batteries and wanted to jump ahead a little to the various use cases for this system. I live in Montana, which as you may guess, we have pretty frigid winters. This leads me to at least two decisions I have to make before going any further on this, but first I should probably provide some insight to my plans with this setup.

The camper itself was stripped of everything (electrical, propane, propane lines, kitchen, heater, fridge, etc.), so it’s basically an empty shell that makes for a perfect drawing board. Knowing that we truly have 4 seasons to endure in this state, I will have some considerations to make in terms of the batteries I want to use, and how I intend to heat the camper.

My initial thought was to go with 2 lithium ion 100ah batteries (maybe Battle Born), but given where I live, they would be below the minimum temperature for charging at least 5 months out of the year. I would highly appreciate some suggestions for how to best go about this, whether that’s forking our additional money for battery heaters, or choosing a different type of battery altogether.

The next question I have is related to actually heating that space. Yes, I know that a pop up camper essentially has zero insulation, but I’ve stayed in one for hunting season when the temp was hovering at 3 degrees Fahrenheit. I’d prefer to have at least a little more comfort than 4 layers of clothes, a -20 sleeping bag, and 3 blankets.

If anyone has suggestions for either of these current obstacles I’ve identified please let me know. Thanks!

I’m no expert here but have a couple of thoughts.

You only need to worry about avoiding charging your batteries below freezing. Discharge should not be a problem. If you can place them anywhere in the living space that may solve the problem.

Electric heat is probably a bad idea. Propane is the likely solution here.

BattleBorn are apparently due to release a series of self-heating batteries, and other manufacturers already have this feature. Keeping the batteries within the living area is also an idea.

Electric oil radiators are generally considered quite efficient and you can get them in all sorts of power ratings (I have a variable up to 750W version for emergencies in my caravan, but generally I only use the 150W setting). If it is powered from the sun, the ongoing energy consumption is still free.

Let's say you needed 150W of heat 24/7, that's 3,600Wh per day. With 3 days autonomy for poor weather, you'd need a 10,800Wh battery bank or 900AH at 12V, and a 3,600W array to power this load during Winter. Augmenting the system with a wind turbine will reduce the PV requirement, as would adding a either a Hydrogen fuel cell or small genset. Or, as @JoeHam says, a small propane heater.

Battery heaters: expensive
Pet bed heaters: cheap

Pet bed heaters use 15 - 75 watts depending on the model and some will run on 12 volts, have thermostats, etc.

Also 12v heated travel blankets draw as little as 45 watts which works out to 30ah for 8 hours of warmer sleep.

So is it possible to keep you and your batteries from freezing at night on 100ah or less.

Battery warming is a well trod subject. A lot of folks are using either pet warmer pads or water tank warming pads. There are a lot of choice / options. A KEY OPTION is to get one that has a thermostat which will turn it On & Off that can be programmed / set. There s no need to cook the batteries, just keep them above 10C/50F and they will be happy as can be. Therefore an insulated box to hold them in is a good idea BUT remember you want to also keep them cool in summer so some sort of "summer mode" venting is prudent.

You mention "pop-up" camper, I'm assuming the ones that have a hard top that you crank up with tent like side ?

Steve_S said:

Battery warming is a well trod subject. A lot of folks are using either pet warmer pads or water tank warming pads. There are a lot of choice / options. A KEY OPTION is to get one that has a thermostat which will turn it On & Off that can be programmed / set. There s no need to cook the batteries, just keep them above 10C/50F and they will be happy as can be. Therefore an insulated box to hold them in is a good idea BUT remember you want to also keep them cool in summer so some sort of "summer mode" venting is prudent.

You mention "pop-up" camper, I'm assuming the ones that have a hard top that you crank up with tent like side ?

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I agree on the thermostat to regulate temperature and only keep the batteries warm enough for optimal use (I.e, 50 degrees F). You’re also correct on the pop up camper. Mine is the slide in camper for a pickup truck. I bought it completely stripped of every amenity, including all kitchen cabinets. So to me, planning a rebuild of the interior has been a little challenging because there’s a lot to consider as I mentioned above in regards to the solar/power/heating portions of the build. I really want to get this all nailed down before building cabinets and everything else.

As you can see, I tore out the old electrical and framed a new wall for the area where I intend to install the solar equipment. If anyone has recommendations for this build, please let me know!

Your certainly deep into it eh ! Damn where that cold one you just had.... ohh gotta get another one... Looks really like a serviceable space there. Pro-Tip there is a product called Mag-O board... It is fireproof, water proof is an excellent tile backer as well it replaces the more expensive & less performant Cement board. It's not the easiest to work with (you have to deep score it to snap it) or use a carbide tipped saw (circ) to cut it (wear a mask !!!!!) and is about 1/2 the price of cement board. Wise to use that round the cooking area... also not bad if you want to build a box that is fireproof... it takes 2000C to affect it. I have used it for tile backer, isolation for fireplaces & woodstove installs, and for tile countertop backer (underlayment) and the stuff is amazing. Put straight MAPP Gas @ 3000C on it and that starts to make it "warm", I know, I did it ! but NOT hot.

Steve_S said:

Your certainly deep into it eh ! Damn where that cold one you just had.... ohh gotta get another one... Looks really like a serviceable space there. Pro-Tip there is a product called Mag-O board... It is fireproof, water proof is an excellent tile backer as well it replaces the more expensive & less performant Cement board. It's not the easiest to work with (you have to deep score it to snap it) or use a carbide tipped saw (circ) to cut it (wear a mask !!!!!) and is about 1/2 the price of cement board. Wise to use that round the cooking area... also not bad if you want to build a box that is fireproof... it takes 2000C to affect it. I have used it for tile backer, isolation for fireplaces & woodstove installs, and for tile countertop backer (underlayment) and the stuff is amazing. Put straight MAPP Gas @ 3000C on it and that starts to make it "warm", I know, I did it ! but NOT hot.

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I’d love to have this project done by the time spring rolls around. But like you said, I’m pretty deep into this project.. Thanks for the MAG-O board tip! I’ll look into this for a backer when I build out the cabinets.

I was contemplating this problem today, myself as I have a 41 foot converted bus on my 165 acres up here in Canada.
I really want to build my own lifepo4 batteries but the cold winter and conversely hot summer makes storing them problematic.
Then I got thinking I wonder if anyone has used a 12v plug in cooler - food warmer that you can buy , to use as an iceless cooler for a battery storage box?
I have no idea if this would drain your battery pack too much or not?
Thanks