NOVELTY - The apparatus (500) has a battery information storage unit (502) for storing battery information concerned with a battery. A charge/discharge information storage unit (503) stores charge/discharge information for charging/discharging the battery. A communication unit (506) receives a communication message concerned with an access request from a charge/discharge instruction apparatus. A control unit (504) controls access from the charge/discharge instruction apparatus based on the battery information, the charge/discharge information and contents of the access request.    USE - Charge/discharge determination apparatus for performing charge/discharge control of a battery based on instructions given from charge/discharge instruction apparatuses in an ordinary home. Can also be used for a building or factory.    ADVANTAGE - The apparatus performs authentication process and access determination process as one and same process, so that quantity of processing, safety and power throughput can be improved efficiently. The charge/discharge instruction unit determines and executes the charge/discharge instruction so as to instruct the battery system to perform discharge control to prevent power failure caused by shortage of power supply or to instruct the battery system to perform charge control to make use of excess power caused by excess of power supply while monitoring quantity and frequency state of supplied power in a system grid of the power producer or on consumer side premises.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a charge/discharge determination method for performing a charge/discharge control of a battery based on instructions given from charge/discharge instruction apparatuses    (2) a charge/discharge determination program comprising a set of instructions for performing charge/discharge control of a battery based on instructions given from charge/discharge instruction apparatuses.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of a charge/discharge determination apparatus.    Charge/discharge determination apparatus (500)    Power supply unit (501)    Battery information storage unit (502)    Charge/discharge information storage unit (503)    Control unit (504)    Communication units (506, 508)