CONTROL DEVICE FOR SECONDARY BATTERY, CONTROL METHOD OF SECONDARY BATTERY, BATTERY SYSTEM, AND MOTOR-DRIVEN VEHICLE

In a control device for a secondary battery, the secondary battery includes a monitoring sensor that detects battery information. An electronic control unit is configured to store first information. The electronic control unit is configured to set a lower-limit state of charge. The electronic control unit is configured to calculate a value of a rate of decrease of a full charging capacity using a value of the full charging capacity and to calculate a value of a state-of-charge variation using the value of the rate of decrease of the full charging capacity and the first information. The electronic control unit is configured to increase the lower-limit state of charge when the value of the state-of-charge variation is greater than a threshold value and to maintain the lower-limit state of charge when the value of the state-of-charge variation is less than the threshold value.