Did you see also https://www.bluetooth.com/specifications/specs/battery-service/ ?
There is a list of services https://www.bluetooth.com/specifications/specs/
@fanoush 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.
Did you see also https://www.bluetooth.com/specifications/specs/battery-service/ ?
There is a list of services https://www.bluetooth.com/specifications/specs/