The present invention provides a battery control system and a battery control method obviating the need for any concentrated control device for controlling the voltage of each unit cell in a battery pack, hardly susceptive to the influence of noise, having a construction not increased, and enabling the load on the control device to be lightened. A unit cell for battery packs is used by interconnecting it to another unit cell and used as a battery pack. The unit cell is composed of a unit cell (5) and a control circuit (1). The unit cell (5) is an electrochemical cell. The control circuit (1) has measuring means (1a) for acquiring cell state information including at least the voltage of the unit cell (5), transmitting means (1f) for transmitting the cell state information outside, receiving means (1f) for receiving outside information, and means (1d) for discharging the unit cell (5) according to the cell state information on the unit cell (5) and the outside information so that the voltages of the interconnected unit cells may approach one another.