Do you guys use anything to check the primary 123's so you know if they need replaced? Other then the light getting dim that is.
I replace them under two circumstances:
A: When I notice them dimming or moon mode kicks in. I don't have any lights that just quit working so I'm always safe.
B: I'm going to clear a building or something and know the batteries are pretty old so I just pop a new set in.
I always make sure I've got a fresh set going into more tactical situations. If I was just working a football game or something simple like traffic stops, I would look for it to dim before I worried.