Putting leaves around the batteries seems impractical. However, it occurs to me that if you buried a coil of 3" tube in a large pile of leaves and then routed that around your storage box with a 'smoke stack' for convection, you might be able to harvest some of the energy of decomposition. The challenge will be to make the pile large enough that you don't freeze the leaves that are adjacent to the coiled tube. (Unfortunately my cabin is in a pine forest and harvesting enough bio-mass would be a challenge. Otherwise I would be tempted to try it.)
Note: This idea came to me while I was looking at an alternative to burying the batteries below the frost line (Also impractical). You could get warmer are from the ground using earth-tubes:
https://milligansganderhillfarm.wor...st-systemto-passivly-heat-and-cool-your-home/
I am not sure if this is practical for my situation either, but it has more appeal than burying the batteries.
Yeah, the problem I have with burying batteries is keeping them dry. Water loves gravity. A ditch is a potential pond.
The leaves thing needs some testing. I have no doubt it works. I just don't know HOW WELL it works, or the best conditions to artificially induce. I keep thinking about the irony of how snow on top allows them to contain and feed off their own heat, like an igloo effect. You think about those really cold nights out of nowhere. How would all that cold quickly get through 18" of snow? It wouldn't. The leaves are protected from wind and have a thick insulation from sudden ambient changes. Yeah, 3 weeks of deep freeze would works its way through. But, those temporary drops wouldn't . You'd have to emulate that type of insulation on top of having decaying leaves. The lid of a cooler by itself is probably not enough.
What we need is real data collecting -- a science experiment with controlled measured variables. But that's a lot of time and money to setup, especially if you want to try different variations over time to find the optimal solution.
I get a ton of leaves on my property. I wish I could donate some to you.
The only thing I can say about pine needles is they make great kindle. When we went camping, we'd try to find them to get a fire going. But, I doubt they work as well for natural decomposition. But, who knows. That would require testing.
I just wish we could find more online on this. You'd think there would be a lot of data on it somewhere. Lithium batteries seem to of created the first really high demand use case. Decaying leaves is just too insignificant of a potential contributor for the needs most care about, like heating a home or cabin. Thus, no one has been collecting data on it.
Farmers with animals have to know something though. They have all kinds of ways of keeping animals alive in barns. Though, barns are also presumabley kept dry, which makes them less than ideal for decomposition.
