The battery compartment cap is made from a medicine cap, circular piece of tin from an Altoid
can, a spring and a laser pointer chain attachment (optional).
The cap contains a piece of cardboard that ensures a air tight seal.This will prevent the mounting of the spring/ tin combination. I removed this and separate both caps from each other. I Soldered the spring to the piece of tin which I cut from an Altoids can. Using a pair of scirrors I cut 2 slots opposite of each other and bend them inward away from the spring assembly. I used a pair of needle nose pliers to bend them. Next,using my soldering iron's heat I melted the both slots into the plastic screw cap through the other side. When the slots were visible from the opposite side I folded them in to secure the tin inside of the screw cap.