The Big Hunting Bore Sight Kit MBS223 comes with a modular battery pack that extends laser run time to 20+ hours. The unit is operable with either the included button cell batteries or the included modular battery pack that uses 2 AAA batteries. This is the system that AimShot recommends be used with arbors for any caliber laser bore sighting. It is the most versitile and accurate system on the market, and should not be compared to any other chamber based bore sights. More accurate, more durable, longer lasting and functionally superior to any other system on the market.