COLD WEATHER BATTERY WARMER

kdwhite67

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Joined
Dec 16, 2020
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24
Hi Folks, I'm pretty new to the solar world and wondering if anyone has any thoughts on how to keep my two 125ah agm batteries warm in the winter here in Minnesota. My tiny house is only heated when I'm there occasionally in the winter. Outside temps can reach -25 fahrenheit and I have freezing concerns. I have thought about using a battery warming pad it would just sit on. Would that work? Or a heater that wraps around the battery?

Any thoughts are much appreciated!
 

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Horsefly

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An AGM battery's susceptibility to extreme cold is very dependent on how fully charged it is. A fully charged AGM or flooded lead acid battery can go down below -70°F. If it is fully discharged though, it will freeze and probably be damaged. But then, a fully discharged AGM is pretty much toast anyway.

At our cabin (Colorado mountains, elevation 9,000 ft) we've left our 4 AGM batteries hooked up to the solar charger to keep it mostly in float through 4 winters now. Hasn't been a problem.
 

kdwhite67

New Member
Joined
Dec 16, 2020
Messages
24
An AGM battery's susceptibility to extreme cold is very dependent on how fully charged it is. A fully charged AGM or flooded lead acid battery can go down below -70°F. If it is fully discharged though, it will freeze and probably be damaged. But then, a fully discharged AGM is pretty much toast anyway.

At our cabin (Colorado mountains, elevation 9,000 ft) we've left our 4 AGM batteries hooked up to the solar charger to keep it mostly in float through 4 winters now. Hasn't been a problem.
Thanks! do you ever use them in the winter? I'm wondering if I need to bring them to room temp (65F) before using them?
 

Horsefly

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Thanks! do you ever use them in the winter? I'm wondering if I need to bring them to room temp (65F) before using them?
Sorry, I didn't see your post.

Unless it freezes, you should be able to use it. The problem with an AGM (vs FLA) is that it probably isn't easy to tell if it is frozen.

Certainly don't try to charge a battery in which the electrolyte is frozen. Even if it does freeze, I've read that you can thaw an FLA or AGM and use it, although it may have lost some of it's capacity.

I think the rule to live by is to keep your AGM fully charged. We keep all our cabin loads off / disconnected during winter, but leave the SCC on. The panels seldom have snow covering them, so the AGMs are kept mostly in float. So unless the basement of our cabin gets to -70°F, they are good to go when someone does show up.

In my case I guess it is kind of theoretical. Our cabin is pretty inaccessible in the Winter, so it certainly hasn't had much use. We've been up in November when it is below freezing, the cabin and the batteries are kept warm when someone is there.
 

circus

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Jul 8, 2021
Messages
271
If you have a root cellar or can insulate a space 4ft below ground (frost line) the temperature usually never go's below freezing. Do you ever have frozen water pipes?
 

Fusion is the future

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Joined
Sep 3, 2021
Messages
143
If you have a root cellar or can insulate a space 4ft below ground (frost line) the temperature usually never go's below freezing. Do you ever have frozen water pipes?
Good idea, what do you think about drilling/digging a deep hole, lay a bunch of copper tubing in it, make a closed circuit above ground Whit a heat air exchanger and the warmer water will flow naturally up, no need for a pump . (thermal circulation )
 
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