I want to share my project "3V AA Battery holder sensor" with you.
I converted a 3V AA battery holder to 3V AAA with the goal to put all the components for a Mysensors node inside the holder. The holder i used can be found here: https://www.mysensors.org/store/batteries
First step was to route the wires to the inside of the holder
Wires are now on the inside of the holder
Remove the metal plate from the holder and cut a new slot. Measure the right distance so AAA batteries will fit.
Put some hot glue in the created gap behind the metal plate.
Put your components on the cover of the holder. In my case a Arduino Pro mini, a si7021 and a NRF module. I also cutted a slot for the NRF so the antenna is outside the holder.