A battery management system and a battery management method are provided. The battery management system includes a temperature sampling circuit, a plurality of voltage measurement circuits, a current sampling circuit, and a microcontroller. The temperature sampling circuit is configured to obtain a temperature parameter of a plurality of battery packs. The voltage measurement circuits are configured to obtain a plurality of open circuit voltage parameters of the battery packs. The current sampling circuit is configured to obtain a current parameter of the battery packs. The microcontroller obtains a plurality of initial state-of-charge parameters of the battery packs according to the open circuit voltage parameters and the temperature parameter and respectively calculates a plurality of present battery powers of the battery packs according to the initial state-of-charge parameters, the temperature parameter, and the current parameter.