Modular battery pack upgrade for existing AimShot 223 laser bore sights. Instead of using the 3 small watch batteries, this allows you to upgrade to the external battery pack that utilizes (2) AAA batteries and will run the red laser for 20+ hr. Fits all AimShot and SpeedAim 223 laser bore sight models. Also a replacement in case something happens to your existing BSB223 laser bore sight. Will not fit the green laser models, please contact AimShot if you have a green 223 laser and need a replacement.