Based on my pwnagotchi and ups-lite using experience I want to propose for consideration using an energy harvester circuit as a part of Flipper power management system.
In brief, energy harvesters is a class of devices, that can collect a very small amount of energy, boost it and store in external supercapacitor and/or rechargeable battery. The source could be almost any device: solar panel even from calculator, TEG-cell, piezoelectric crystal, or, bringing closer to project specifics, any antenna or coil, which are enough in Flipper.
The logic of usage is based on conclusion, that operator will use only one task at once. Therefore, scanning a wifi or bluetooth keeps NFC, 433MHz and RFID antennas free to receive any electromagnetic waves to charge supercap and internal battery. In case of any antenna is used, the transistor switch disconnects it from energy harvesting circuit.
As the supercapacitors have very small internal impedance and charges very quickly, much faster, than batteries, operator can charge device from any rfid-reader, radiowaves source or cheap always-on wireless charging stations for mobiles, thus getting Flipper a device, that in some circumstances doesn’t require charging at all.
Harvested energy should be enough to keep LPMCU running forever and drain excess to main battery. I can’t bring exact energy calculations using proposed device because Flipper developers decided to switch from RPi to another system board with unknown power consumtion and I still waiting my engineering sample from the Chinese post to be delivered.
But I will, if this idea finds a support between Flipper engineers.
So as not to be unsubstantiated I did some pre-research and decided to test a Texas Instruments BQ25570 energy harvester chip.
Take a close look to datasheet: https://www.ti.com/lit/ds/symlink/bq25570.pdf
and bit of practical application with some calulations:
https://www.lab4iot.com/2019/07/29/energy-harvesting-tutorial-with-the-ti-bq25570-part-1/