The battery management unit for a vehicle includes a charger mounted on the vehicle, configured to connect to an external power source and charge an assembled battery including a plurality of cells with electric power from the external power source; a memory that records which cell is a lowest cell having the lowest voltage when the battery is fully charged; and a cell-balancer that carries out cell-balancing on the voltage of the battery by discharging, when the charger is not charging the battery, the cells having a voltage higher than a current voltage of the lowest cell to the current value of the lowest cell.Thereby, it is possible to suppress an increase in dispersion of voltages and reduction in battery capacity.