Battery & Canister
I create the canisters for my diving lights from UV-resistant PVC pipe by making a plug for the base out of flat stock on the CNC.  I epoxy it in place and finish it on the lathe.  I then dye it using a solvent based dye then add hardware.  The batteries are welded together from NiMh D cells and then fitted with machined lids and bases with 3 aluminum rods holding the assembly together.  The can lids are made from acrylic and form a two piece design that traps water in the event of a cord tear or punctured switch boot, therefore protecting the batteries.  My lights have seen action in the caves of Florida and the Yucatan Peninsula as well as the depths of the local Hawaiian waters.