AimShot's Modular Battery Pack is an upgrade for your 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. It is also a replacement in case something happens to your existing BSB223 laser bore sight. This model fits all AimShot and SpeedAim 223 laser bore sight models. It will not fit the green laser models.