I think the best solution is to just vary the voltage. What do you think? That is, reduce and increase the voltage if I want it more or less cold or hot.
https://www.amazon.com/-/es/dp/B08XJV1HS6/
Those batteries commonly used for drones are small, light and powerful (18000 mAh at 14.8V is about 20000 mAh at 12V). If I lower the voltage more, it will last longer because of the lower consumption, right?
I have not tested the batteries yet, on paper everything is beautiful. But, before buying the batteries (the most expensive) I would like to have other opinions.