Had an issue today I had never had with the KAC battery cap. Started getting intermitent malfunction on the red dot, and remembered I only had one battery in it from a recent replacement. The active battery in the clamps had started wiggling loose, because it didn't have the tension of another replacement battery with the rubber ring to keep it secure.
Something to think about when you replace a battery. Make sure you top it off with the second battery to avoid issues down the road.