NOVELTY - The apparatus has a load data collection unit (1-1) to collect load data in a power system. A component extraction unit (1-3) is used to extract the data from load data components larger than a predetermined frequency. A control unit (1-5) controls a battery based on the components. The predetermined frequency is taken to be a frequency larger than the predetermined frequency. The load data collection unit collects components ranging from the former frequency to the latter frequency.    USE - Battery control apparatus for controlling battery connected to power system connected with distributed power generations e.g. photovoltaic power generation and wind power generation.    ADVANTAGE - The apparatus reducing power flow fluctuations in a distribution system connected with batteries. The apparatus ensures that extraction of the intermediate-cycle components allows for an efficient control of the batteries. The apparatus can reduce the capacity of the battery and produce appropriate specifications of the battery. The installation of the battery in a section between a feeder and a branch point of a high-voltage distribution line or in a section between a pole-mounted transformer and a branch point of a low-voltage distribution line can reduce the capacity of the battery and the line capacity of the distribution line, thus alleviating the burden on the distribution lines leading to a reduced facility management cost. The apparatus reduces the burden on a power system equipment such as transformer capacities and distribution line capacities when the fluctuation components can be absorbed by the batteries.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a battery control method    (2) a battery specification determination method.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of a battery control apparatus.    Load data collection unit (1-1)    Component extraction unit (1-3)    Control unit (1-5)    Battery (13)    Feeder (16)