Hi my name is Egidijus, Your project is interesting for my, so I could help you, cause have exact experience for it. I am working on PCB design with altium and AVR programming is C, so to make your project there is no problem. Okey, so what would be your battery, maybe standard 18650 would be good ? Is it okey to use Atmega48PA ? Do the temperature point should be controlled by outside, or just written in the code ?