A hub apparatus (100, 200), comprising: a rotor assembly comprising: a first housing component; a second housing component positioned opposite to the first housing component, the first and the second housing components (101, 201) together define an internal space; and a plurality of magnets mounted on one or both of the first and second housing components (101, 201); a shaft positioned to extend through the rotor assembly, the rotor assembly being rotatably coupled to the shaft; and a stator assembly fixedly coupled to the shaft and positioned in the internal space, the stator assembly comprising-- a coil assembly fixedly coupled to the shaft, the coil assembly being positioned corresponding to the magnets; a main circuit board fixedly coupled to the coil assembly; and a battery assembly positioned inside the coil assembly and carried by the main circuit board, the battery assembly including a plurality of battery packs circumferentially positioned about the shaft; wherein the rotor assembly is configured to rotate relative to the stator assembly based on a signal from a controller carried by the main circuit board; wherein the battery packs are positioned in a reference plane generally perpendicular to the shaft; the hub apparatus characterized in that: a longitudinal direction of each of the battery packs lies in the reference plane; and the first and second housing components (101, 201) are configured to be tightly fitted with each other by an insertion flange formed on the second housing component, and the insertion flange is configured to be inserted into a gap between the magnets and an inner circumferential surface of the first housing component. a rotor assembly comprising: a first housing component; a second housing component positioned opposite to the first housing component, the first and the second housing components (101, 201) together define an internal space; and a plurality of magnets mounted on one or both of the first a first housing component; a second housing component positioned opposite to the first housing component, the first and the second housing components (101, 201) together define an internal space; and a plurality of magnets mounted on one or both of the first and second housing components (101, 201); a shaft positioned to extend through the rotor assembly, the rotor assembly being rotatably coupled to the shaft; and a stator assembly fixedly coupled to the shaft and positioned in the internal space, the stator assembly comprising-- a coil assembly fixedly coupled to the shaft, the coil assembly being positioned corresponding to the magnets; a main circuit board fixedly coupled to the coil assembly; and a battery assembly positioned inside the coil assembly and carried by the main circuit board, the battery assembly including a plurality of battery packs circumferentially positioned about the shaft; a coil assembly fixedly coupled to the shaft, the coil assembly being positioned corresponding to the magnets; a main circuit board fixedly coupled to the coil assembly; and a battery assembly positioned inside the coil assembly and carried by the main circuit board, the battery assembly including a plurality of battery packs circumferentially positioned about the shaft; wherein the rotor assembly is configured to rotate relative to the stator assembly based on a signal from a controller carried by the main circuit board; wherein the battery packs are positioned in a reference plane generally perpendicular to the shaft; the hub apparatus characterized in that: a longitudinal direction of each of the battery packs lies in the reference plane; and the first and second housing components (101, 201) are configured to be tightly fitted with each other by an insertion flange formed on the second housing component, and the insertion flange is configured to be inserted into a gap between the magnets and an inner circumferential surface of the first housing component. a longitudinal direction of each of the battery packs lies in the reference plane; and the first and second housing components (101, 201) are configured to be tightly fitted with each other by an insertion flange formed on the second housing component, and the insertion flange is configured to be inserted into a gap between the magnets and an inner circumferential surface of the first housing component.