A battery assembly includes a battery holding unit and a battery unit removably held by the battery holding unit. The battery unit includes a battery, a first engaging portion and a second engaging portion disposed on an end portion of the battery. The battery holding unit includes a holding member selectively engaging with the first engaging portion or the second engaging portion to hold the battery unit at a first position or a second position. When the holding member and the first engaging portion relatively move away from each other, the battery unit moves from the first position to the second position at which the holding member engages with the second engaging portion, and the second engaging portion is allowed to rotate along a surface of the end portion to disengage from the holding member and to remove the battery unit from the battery holding unit.