A discharge and charge control system is a discharge and charge control system of a non-aqueous electrolyte secondary battery provided with a positive electrode including a composite oxide containing lithium and nickel. This system comprises: a discharge and charge circuit that discharges the secondary battery, and charges the secondary battery by electric power from an external power source; and a control device that controls the discharge and charge circuit so as to obtain a voltage within a voltage range in which the voltage of the secondary battery has the predetermined discharge final voltage as the lower limit and the predetermined charge final voltage as the upper limit. The control device changes at least the discharge final voltage depending on the variables related to the deterioration of the secondary battery.