In a charge/discharge control method of a lithium ion battery having a negative electrode active material and connected to a charge/discharge control device, battery information regarding a charge/discharge state of the lithium ion battery is acquired by the charge/discharge control device, a degradation state of the lithium ion battery is determined on the basis of the battery information, by the charge/discharge control device, and a voltage range for charge/discharge of the lithium ion battery is changed on the basis of a determination result of the degradation state, by the charge/discharge control device.