There's an option to 'Calibrate battery' under Utils in the settings on the watch, have you tried that?
@Ganblejs started
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
There's an option to 'Calibrate battery' under Utils in the settings on the watch, have you tried that?