A wheelchair drive unit 10 attachable to a wheelchair for assisting the propulsion thereof comprises: a gearbox 11 having opposed side faces 15 each provided with an axle 30 for carrying a ground-engaging wheel, a motor mounting means 35 by which an electric motor 12 may be coupled to the gearbox to drive the ground engaging wheels, and a battery support 13 for carrying a battery adapted to power the electric motor. The battery support may be made of plastics material and may be unitary molded. The battery support may also be releasably connected to the gearbox. The battery support may include a locating region 42 for housing an electrical unit interfacing the battery, the motor and a controller. The gearbox may house a worm drive.
