Battery system

A battery system manages a plurality of battery cells of an assembled battery. The battery system includes at least a plurality of battery cell management units which is connected to the battery cells and manages the connected battery cells. The battery cell management units are connected to each other. Each of the battery cell management units comprises at least an operation mode switching unit, a parameter-related data generating unit, a parameter data transmitting unit, a parameter data receiving unit, a minimum value specifying unit, a switching command data transmitting unit, and a switching command data receiving unit.