Roombas run on a rechargeable NiMH battery. The Roomba Red battery pack is rated at 3 amp-hours and takes about seven hours to fully charge to about 18 volts. Some of the more recent Roomba models have cut that charge time down to about three hours. A full charge equals approximately two hours of cleaning time, which in the Roomba world means vacuuming three medium-size rooms before it needs to rejuice. The mobility system consists primarily of two motor-driven, tracked wheels. Roomba steers by alternating the power supplied to each wheel.