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 two AAA batteries and will run the red laser for 20+ hours. 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.