Replace the LR44 with a AAA battery for the Generic caliper. the battery is fiction fit with the bend on the side of the battery compartment.
You will need: wires, tinfoil, some type of glue and a multimeter
 

• Route 2 wires to the slot of the battery cap. Use a dab of glue to secure it in the slots.
• Glue a piece of tin foil to the bottom of the cap making sure the tinfoil is making contact with the wire
• Slide the cover onto the caliper
• Slot the cap into the cover, push it down and rotate anti-clockwise. The prong will hold it in place
• Slide the cover out abit and use a tool to pry the side prong towards the cap. then slide the cover back
• Route the wire to both end of terminals 
• Add tinfoils to terminals
• optionally add a dab of glue to hold the wire flat and tinfoil down.

PS: There are 3 offset sizes for the battery cap, I use the 0.4mm, but I would recommend 0.5 or 0.6mm. Hot glue is your best friend here, use a flathead to smear the glue will help alot