for a few years now i’ve been struggling with the Xiaomi sensors battery replacement and for this wanted a solution so that i’d never have to replace the battery’s again. with a little help i found what i was looking for.
first off i drilled a hole in de side of the casing:
then i soldered the ground and the 3.3v output pin from a voltage reducer to the battery contacts:
Voltage reducer 4.5-24V to 3.3V : Link
then i hot glued the cable and connected the - to the - of the sensor:
then solder the + from the usb cable to the imput of the reducer:
now connect the usb-cable to a wall-socket/power supply and press the connect button to see it work.
after this i used some UV-Resin to make sure the cables are not connecting when something moves(few drops) and UV glued the cable to the side of the case:
this way the battery lid can still be closed, the unit will never go into power-save, will never disconnect and reports to homey correctly.
let me know if you have any suggestions or better ideas