Abnormal Cell Diagnosing Method and Battery System Applying the Same

A battery system includes: a battery pack including a plurality of battery cells; and a battery management system for setting numbers to the battery cells by measuring cell voltages of the respective battery cells at a wake-up time, detecting a maximum cell voltage and a minimum cell voltage by periodically measuring the cell voltage of the respective battery cells after the wake-up, comparing the minimum cell voltage and the cell voltage of at least one first diagnosis target battery cell, comparing the maximum cell voltage and the cell voltage of at least one second diagnosis target battery cell, and diagnosing whether the diagnosis target battery cell is abnormal according to results of the comparison.