A charge/discharge control system for controlling charge/discharge of a non-aqueous electrolyte secondary battery having a positive electrode including a composite oxide containing lithium and nickel. This system includes a charge/discharge circuit for discharging the secondary battery and charging the secondary battery with power from an external power source; and a control unit for controlling the charge/discharge circuit such that the voltage of the secondary battery is within a voltage range having a predetermined end-of-discharge voltage as a lower limit value and a predetermined end-of-charge voltage as an upper limit value. The control unit is configured to change at least the end-of-discharge voltage according to a variable related to deterioration of the secondary battery.