A bicycle electric rear derailleur that has a support body configured to be mounted on a bicycle frame at an assembly of wheels coaxial with a hub of a rear wheel of the bicycle, a movable body, having a chain guide and linkage between the movable body and the support body. The linkage between the movable body and the support body comprises an inner connecting rod and an outer connecting rod. The ends of the rods are articulated to the support body and to the movable body to form an articulated parallelogram. A battery power supply unit is supported by one of the inner connecting rod and the outer connecting rod.