Modular Battery Pack upgrade for existing AimShot BS30 30 Carbine laser bore sights. Instead of using the 3 small watch batteries, this allows you to upgrade to the external battery pack that utilizes two AAA batteries and will run the red laser for 20+ hours. Fits all AimShot BS30 laser bore sight models. Also a replacement in case something happens to your existing MBS30 laser bore sight. This is just the replacement battery box and end cap for the BS30 laser bore sight.