I have a feeling there's a whole lot I don't know about batteries.
My my current project where the setup consists of an ATmega328, a nRF24Lo1 and a DHT22. I wanna put is on my ceiling with no intentions of ever retrieving it. So, no need, paying for rechargeables.
I was thinking 4 x 3.3V baterries @ 1000mAh each. But parralizing 4 lithium batteries on my flammable ceiling isn't too comforting.
If I wan't something like 4000mAh what would your suggestions be?
My current choice is this battery.
I don't know about the DHT22 but the Atmega 328 plus nRF24 works very nicely on 2 x AA Alkaline cells and (though I have not tried it) would probably work with two NiMh cells. Use bigger cells if you need more energy.
I can't figure from this "So, no need, paying for rechargeables." whether you do or do not plan to recharge the cells.
3.7v (or 4.2v fully charged) would be no problem for the Atmega 328 but would be too much for an nRf24. You could use one or two diodes in series to drop the voltage.
...R
If you never plan on retrieving the project and are afraid of flammable batteries, why not just use a wall power supply?