An apparatus of estimating a degree of aging of a secondary battery, the apparatus comprising: a current measuring unit configured to measure a current of the secondary battery and output a current measurement; a temperature measuring unit configured to measure a temperature of the secondary battery and output a temperature measurement; and a control unit operatively coupled to the current measuring unit and the temperature measuring unit, wherein the control unit is configured to: determine the current and the temperature of the secondary battery by receiving a current measurement signal and a temperature measurement signal respectively from the current measuring unit and the temperature measuring unit; determine a state of charge of the secondary battery from the current of the secondary battery; characterised in that the control unit is configured to determine an operation state of the secondary battery as one of a calendar state and a cycle state by using the current of the secondary battery; determine a degree of calendar aging in the calendar state by applying a cumulative degree-of-aging model to a predefined degree-of-calendar-aging profile corresponding to the determined state of charge and the determined temperature while the secondary battery is in the calendar state; determine a degree of cycle aging in a cycle state by applying the cumulative degree-of-aging model to a predefined degree-of-cycle-aging profile corresponding to the state of charge, the temperature, and the current of the secondary battery while the secondary battery is in the cycle state; and determine, as the degree of aging of the secondary battery, a weighted average value that is calculated for the determined degree of calendar aging and the determined degree of cycle aging on the basis of calendar time for which the calendar state is maintained and cycle time for which the cycle state is maintained. a current measuring unit configured to measure a current of the secondary battery and output a current measurement; a temperature measuring unit configured to measure a temperature of the secondary battery and output a temperature measurement; and a control unit operatively coupled to the current measuring unit and the temperature measuring unit, wherein the control unit is configured to: determine the current and the temperature of the secondary battery by receiving a current measurement signal and a temperature measurement signal respectively from the current measuring unit and the temperature measuring unit; determine a state of charge of the secondary battery from the current of the secondary battery; characterised in that the control unit is configured to determine an operation state of the secondary battery as one of a calendar state and a cycle state by using the current of the secondary battery; determine a degree of calendar aging in the calendar state by applying a cumulative degree-of-aging model to a predefined degree-of-calendar-aging profile corresponding to the determined state of charge and the determined temperature while the secondary battery is in the calendar state; determine a degree of cycle aging in a cycle state by applying the cumulative degree-of-aging model to a predefined degree-of-cycle-aging profile corresponding to the state of charge, the temperature, and the current of the secondary battery while the secondary battery is in the cycle state; and determine, as the degree of aging of the secondary battery, a weighted average value that is calculated for the determined degree of calendar aging and the determined degree of cycle aging on the basis of calendar time for which the calendar state is maintained and cycle time for which the cycle state is maintained.