Apparatus and Method for Diagnosing Degree of Degradation of Battery

An apparatus for diagnosing a degree of degradation of a battery includes a measuring unit configured to measure a voltage of each of a plurality of battery cells in each of a plurality of cycles where charging and discharging is performed and output voltage information about the plurality of measured voltages, and a control unit configured to receive the plurality of voltage information, calculate a voltage deviation of each cycle for each battery cell based on a reference voltage of each of the plurality of battery cells, select a cycle section satisfying a predetermined condition for each of the plurality of battery cells based on the calculated voltage deviation, calculate a voltage deviation change rate corresponding to each of the plurality of selected cycle sections, and diagnose a relative degree of degradation of the plurality of battery cells based on the plurality of calculated voltage deviation change rates.