MARINE POWER SUPPLY SYSTEM

A marine power supply system (3) includes a battery unit (30, 230) including a first battery (33) configured to supply power to a starter (25) configured to start an engine (21), and a second battery (34, 234a) configured to supply power to an electric motor (22), and a power distributor (5, 31, 36, 53, 205, 231, 236, 305, 331) connected to the first battery and the second battery. The power distributor is configured to output a demand power amount of power required by the first battery to the first battery, and to output at least a portion of surplus power to the second battery when a total demand power amount required by the battery unit includes the surplus power.