I have a green laser aiming device on my AR-15. It has an aluminum milled body which holds two CR 123 cells with a heavy aluminum cap at the end. I press check it often. I am alarmed when I come back the next day and it doesn't work. I used to clean the inside of the cap, the part that contacts the positive side of a cell, to restore its reliability. I don't clean it anymore: I use a conductive grease coating instead.
Most of the lighting products and laser products associated with firearms have been made of machined metals. These products are usually made of brass, aluminum, and steel, in various combinations. They are reinforced to survive recoil and shocks from dropping. Aluminum is usually the culprit. If your product uses the body or endcap to conduct electricity, consider this: oxidation can take place in a day, especially on aluminum parts. If you coat the product with dielectric grease, it will fail. Use the kind of grease used to prevent oxidation in household wiring instead. This is sold under various names.
I use OX-Gard, a trademarked product. It is simply grease that conducts electricity. Put a thin coat on areas where aluminum has to conduct electrical current. In case anyone was wondering: A one-ouunce (28g) tube is good for the entire department inventory, for several years.