Battery system

A battery system configured to charge and discharge electric power, the battery system comprising:

• a battery pack in which a plurality of battery cells is connected in series;
• a plurality of detection lines each configured to detect a potential of a corresponding one of the battery cells;
• and
• a processor configured to monitor voltages of the battery cells each determined from potentials of corresponding ones of the detection lines, wherein:
• the battery cells include a first battery cell and a second battery cell;
• and
• the processor is configured to
• detect an abnormality in voltage detection based on an open-circuit voltage difference when a current flowing through the battery pack is smaller than a predetermined small value, the open-circuit voltage difference being a difference between a first open-circuit voltage of the first battery cell and a second open-circuit voltage of the second battery cell, and
• detect an abnormality in voltage detection based on a closed-circuit voltage difference when an amount of variation in the current flowing through the battery pack is smaller than a predetermined amount, the closed-circuit voltage difference being a difference between a first closed-circuit voltage of the first battery cell and a second closed-circuit voltage of the second battery cell.