We recently received this question from Lucas Ginter of Bozeman, Montana about lithium batteries and solar power system sizing.
I recently bought a 2004 Bigfoot 2500 10.6E truck camper and I am working on putting in new batteries and a solar charging system on it. I am relatively new to truck campers, but I do have a little experience with solar charging systems and types of batteries. I read your articles on truck camper batteries, solar power, and lithium battery heating systems.
I want to buy the best solar charging system and batteries that will work for my needs. I live in Bozeman, Montana and my plan is to use the camper during the winter months to camp and back country ski out of the camper and use the camper in the summer to rock climb and mountain bike out of. This mean that my batteries will have to be able to survive temps of -20 to 100 degrees F and I would prefer to not have to not buy a generator.
I want to be able to use the lithium batteries because they seem superior to the other types of batteries, but I am wondering how well insulated I would have to make my battery compartment and how many heating pads I would need in order not to kill them when I am camping in below freezing and below zero weather. What do you think?
If you don’t think I can do the lithium batteries I was thinking that two to four Lifeline AGM 6-volt deep cycle batteries would be my best bet. Would you still recommend insulating the battery compartment and heating it?
Finally, I am looking to get two to three 60 cell monocrystalline solar panels each with its own micro inverter for a total of 800 to 900 watts. My friend who works in solar power in Montana recommended the REC N-Peak solar panels because of their durability and high efficiency. I was thinking that 900 watts would be good for me, so I could charge up during the limited daylight that we get in Montana in the winter. What do you think? Any and all advise would be greatly appreciated!
Hi, Lucas. These are great questions. Let’s address the lithium (LiFePO4) battery question first. As you know, charging lithium batteries below 32 degrees F can cause irreparable damage to them, a costly mistake when you consider how expensive lithium batteries are to begin with. Yes, you can still use lithium batteries below freezing, you just can’t charge them below that temperature. An important thing to keep in mind, however, is that this temperature restriction relates to the temperature of the battery and the compartment they are stored in only. Thus, storing lithium batteries inside would be a much better solution compared to an outside storage compartment where they can be exposed to extreme temperatures. So if you can store lithium batteries inside your camper, I would buy them because the pros of lithium far outweigh the cons. However, if storing them inside isn’t an option for you, I would bypass lithium and go with AGM batteries instead.
How large of a battery system should you build? If you have the room, I would buy four AGM 6 volt batteries like those made by Lifeline. These lead acid batteries are true deep cycle batteries with heavy internal plates. Indeed, each 6-volt battery weighs a whopping 66 pounds, twice the weight of a Group 24 lithium battery like those made by Expion360. These 6 volt batteries provide an impressive 220 amp hours total. But remember, when you wire 6 volt batteries in series to obtain the needed 12 volts, the amp hour total remains the same, so a total of four 6 volt batteries will provide you with 440 amp hours (a series-parallel wiring configuration). Unfortunately, as is the case with all lead acid batteries, only 50 percent of this total will be usable. Since even lead acid batteries perform better when warm, I would insulate the compartment and maybe build a heating system like the one we outlined recently for lithium batteries.
As for the size of your solar power system, it depends on the size of your battery bank. For truck campers, we normally recommend one 120 watt solar panel per 120 amp hour battery, but this is for southern latitudes that receive lots of sunlight like where we live in Arizona. For someone who lives in the northern latitudes or areas with limited sunlight, like in the Pacific Northwest, we recommend doubling the size of your solar power system. So if your battery bank consists of four 6 volt AGM batteries (440 amp hours total), we recommend installing a solar power system with at least 880 watts of solar panels. Something like 700 watts mounted on the roof and two portable 200 watt solar panels that can be aimed directly at the sun would be ideal (unfortunately, the real estate found on truck camper roofs is pretty limited so you might not have room for 700 watts). These panels should be controlled by one solar charge controller in order to prevent “dueling” charge controllers, something that we’ve written about extensively in previous articles.
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