Thermal switch recommmendations

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Jan 5, 2022
I'm using a small-ish 3s lithium ion pack to power some outside shed lights, nothing too complicated. I want to have a better pack for next winter and I want to keep the batteries warm when it gets below freezing. There are suggestions for building out a large battery storage with insulation and large heaters during the winter. This is just for a small pack.

I'd ideally like to put the pack in a small box (roughly shoebox size?), insulate the box, and run a peltier module or two directly off the pack. Can someone suggest a thermal switch for cheap that would work in this application? I was thinking, peltier module connected to the battery via a NO relay, triggering temperature 0 degrees celsius, module turns on, warms the pack to 5 degrees, relay switches back open. Repeat until the remains of the horse are thoroughly beaten. Or till spring, whichever comes first.

Can someone suggest a simple switch or relay for this application? There's probably a dozen ways to do it, and I won't need it till next winter, so I'm open to suggestions.