Designed to be used with an external battery pack our battery bore sight systems provide the extended run time that the traditional bore sight cannot. Allowing the operator 20+ hr of run time off 2-AAA batteries this system offers the most economical solution for all your bore sighting needs. The external battery bore sight system is intended for use of only open chamber applications. Severing the wire will render the laser inoperable. This product is the 17 HMR laser bore sight module with external battery box. Designed to make it quick and easy to bore sight your rifle chambered in 17 HMR. Features: Battery pack utilizes (2) AAA batteries Approximately 20+ hr in runtime Wire approximately 3 inches in length