I might order one at least to test with. Condensation may be challenge just like with freezers or fridges. Although in a sealed box there shouldn't be that much moisture available.
I wonder how much power is needed to keep insulated box at around +20...25 °C if the outside temperature is about +25...30 °C at maximum. At those temperatures there are probably excessive amount of solar energy available so 50 or even 100 W should not be a problem.
I can test this for you!!
I have a 24v (8s) plywood case with two 75W silicone heating pads inside, connected to a digital control. I set the operating range pretty wide so the heater only cycles a few times per hour - well depending on the temperatures outside.
This DIY pack runs an MPP2724 mobile pack for tools and things around my property or mounted in the bed of my truck as a mobile 20A outlet to go.
A few weeks ago I ran my MIG welder on this set up, while building my next PV array racks, and the heating function just cycled on and off to hold the temperature inside the case at about 15-degrees-C while it was about neg 15C outside. I remember watching the cycle time, to get an idea of the energy used, and the "on" time was only about five minutes, about once every 30-45minutes or so. The box is not insulated - just 19mm plywood.
The loads on the battery were near to my max 20A-120v output for the inverter, ie 80A from the cells, which would aid with keeping them warm I suspect. Would be interesting to just put the battery outside, turn on the heating function and measure energy used for a period of 8-hours, with no loads affecting the numbers.
Some 50mm polystyrene insulation would reduce the heating requirement considerably. I am working on an removable insualted box option.
I can do a more detailed test this weekend if you would like the data collection, just let me know.
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