1. Solder wire from PCB's battery wire connectors to the battery holder
2. Screw PCB and battery holder onto the acrylic sheet using M3 screws
3. Attach an acrylic sheet to the wall with 3m Mushroom Dual Lock Self Adhesive Tape

I am trying out a ghetto mounting on a wall that I cannot really drill. Masking tapes are not really for long term :p