Abstract: A package operable to provide power assist to a pedal operated vehicle having a rear wheel, the vehicle movable longitudinally, comprises: a) a carrier b) a ground engaging drive wheel supported by the carrier and at least one electric battery and an electric battery operated drive supported by the carrier to rotate the drive wheel, c) the carrier coupled to the vehicle for up and down pivoted movement about a generally lateral axis in close association with the vehicle rear wheel, d) the battery or batteries and at least part of the drive being located vertically above the drive wheel so that the weight of the carrier, the battery or batteries, and at least part of the drive bears downwardly on the drive wheel to urge the wheel into ground engagement.