The present invention relates to a drive unit in the form of a caravan mover (10) comprising a motor (12) (drive means) and a head (14) which are linked together by a gear mechanism (16). The head (14) provides a roller (15) which is rotatably mounted on a shaft. The roller (15) is arranged, in use, to be urged or pressed against the tread portion (surface) of a tyre. The drive unit is controlled by a control unit (ECU) which controls the movement of the driven roller (15) between the disengaged position and the engaged position and also controls the rotation (and direction) of the driven roller (15). The caravan mover (10) of the present invention includes an integral power supply such that the unit comprises a single integral system which is easily installed on the caravan and does not require the routing of cables from a remote power supply. The battery (30) comprises securement means in order to quickly and easily secure the battery (30) to the drive unit housing and, in particular, to the housing (20) of the motor (12). The securement of the battery (30) to the motor 6 also automatically and simultaneously aligns and connects terminals of the battery (30) to power receiving terminals of the motor (16). Such a quick and simply securement mechanism provides a battery (30) can be quickly and easily removed, for example, in order to be charged. Accordingly, the drive unit/caravan mover (10) (including the motor, roller, battery, control unit and mounting means) forms a single self-supporting component which is solely secured to the caravan/trailer at a single location by the mounting means.