The RoboMow spare power pack is an extra battery for the RoboMow robotic lawn mower. This battery recharges in just 6 hours with the rapid external charger. With a power equivalent of a 5.5-horsepower motor, it will power the RoboMow lawn mower for 2-1/2 to 4 hours. Use it while the main battery recharges: you"ll never have to let your lawn overgrow while waiting for a battery to charge again. The spare power pack measures 13-by-12-by-11 inches and weighs 32-1/2 pounds.