[kilpikaarna]

Can't claim to know the specifics, but there's some supporting links for both the battery and bootloader stuff in the article. The supercapacitor (can be a regular cap too, but would be physically much larger) is for buffering the power supply to prevent the device from shutting off if there's a momentary draw that causes the voltage to drop.

[dtj1123]

I appreciate what you're saying here, but what I'm asking about isn't the set of solutions to the problems described in the article. What I'm interested in is the underlying mental model of how this kind of device works.

[throw_me_uwu]

Just play with electronics, Arduino/Raspberry/ESP32-compatible stuff is cheap and available. Lots of information about it. A phone is not that much different from a microcontroller board on a battery.