A marine propulsion device, including an engine including a crankshaft, and a power generator including a rotor configured to be rotated by the crankshaft, and a stator arranged to face the rotor, the stator including a first coil group and a second coil group each configured to generate alternating current (AC), the second coil group being configured to generate more electric power than the first coil group. The marine propulsion device further includes a rectifier configured to rectify the AC generated by the first coil group to thereby obtain a first direct current (DC), and to output the first DC to a first battery, a converting device configured to convert the AC generated by the second coil group into a second DC, and a transformation device configured to transform a voltage of the second DC, and to output the voltage-transformed DC to a second battery.