I wasn’t happy with the battery life of the Xiaomi LYWSD03MC temperature sensor with Zigbee firmware, so I decided to make a AA battery “backpack” that replaces the standard CR2032 coin cell.

Remove the back cover of the temperature sensor before inserting it in the battery pack. I attached it with some double sided tape, to make sure that it doesn't come out.

The case fits 2 AA batteries, but you need to add the physical connections to the sensor yourself. I did it the simple way by attaching the contact points to the batteries using sticky backed conductive tape. You can also choose to use wires, but that probably involves soldering. 

Note: There's a straight and a (10°) tilted version. They both fit the same lid.