I used 3 xiao ble microcontrollers, one for each side plus one for an optional dongle.

The NFC pads on the microcontroller needs to be used.

Each switch needs a diode.

Optionally you can use kailh hotswap sockets.

The batteries I used are https://ecocell.com.au/product/lipo-1100-603450/ they are about 50mm x 34mm x 6mm.

I stuck the batteries to the bottom plate with double sided tape and put a thin piece of foam between it and the switches, just in case.

Use the included proto files to fine tune your printer settings and if needed the file so that everything fits nicely.

For me I used a bottom layer height of 0.2mm and then the rest at 0.12mm.

https://github.com/MoltenZaz/zmk-config-hwelora