This is bundle of 2 items, a Priority Start 12V H.D. battery protector and a Priority Start holster. The 12V ProMax H.D. from PriorityStart! is the only automatic computerized on/off protection system for your battery, alternator, and electrical system on the market today. It recognizes when your battery’s voltage drops to 11.7 volts, and then disconnects so that the battery’s voltage can recover. The 12V ProMax H.D. offers heavier load capacity (up to 1,600 starting amps/400 continuous amps) for the effectiveness you want.