wolframore:
Wondering if I missed something.
Quite a bit.
If you run your ?"Atmega chips"? on 8Mhz then you can power them with a single LiPo cell (no regulator).
The newer/longer TP4056 charger boards have buildin battery protection.
An "Atmega chip" can measure it's own supply internally (code only), to shut down (sleep) before the protection kicks in.
Leo..