It seems that charging up to 80% is used in electric vehicles to increase durability.
@jon_slider once gave me extremely helpful articles about it :
BU meta description needed...
batteryuniversity.com
BU meta description needed...
batteryuniversity.com
It would be cool if there was a flashlight with built-in batteries and a built-in charger that would charge it up to 4V and switch to super-saving mode at 3.7V (run 1 level, max 5-8 lm). It would make a very reliable flashlight, but manufacturers of batteries and flashlights are hardly interested in this. If there is an almost eternal device, then who will buy a new one, and where will the money come from to develop better batteries and flashlights?
It is necessary to make sure that the battery dies after 300 cycles or after 1.5 years of use (and the LED after 3 years). And it is necessary to agree on this between all manufacturers, as was once done between manufacturers of incandescent lamps.
For example, something oval, similar in appearance to Lupine Piko TL, but with a usb-c built-in charger for built-in 2 * 21700, reflector + TIR (a mule-COB 25-30 degress and something like XHP50.3 HI 7-12 degress for medium range), 2 buttons for separate control of emitters.