BATTERY DIAGNOSIS APPARATUS, BATTERY DIAGNOSIS METHOD AND ENERGY STORAGE SYSTEM

A battery diagnosis apparatus according to the present disclosure includes a voltage measuring unit to measure a cell voltage of each of first to nth battery cells and a control unit, wherein n is a natural number of 2 or greater. The control unit determines an average cell voltage of each battery cell for a first rest period from a first time point to a second time point, based on the cell voltage of each battery cell measured a first number of times for the first rest period. The control unit determines an average cell voltage of each battery cell for a second rest period from a third time point to a fourth time point based on the cell voltage of each battery cell measured a second number of times for the second rest period. The control unit diagnoses a fault of each battery cell based on the average cell voltage of each battery cell for the first rest period and the average cell voltage of each battery cell for the second rest period.