Provided is a battery system having improved safety and reliability. The battery system includes a battery module including a unit cell and a cell controller performing control of the unit cell and a battery controller performing control of the battery module; the cell controller includes an abnormality diagnosis unit which diagnoses the presence or absence of abnormality of the unit cell, a state detection unit which calculates any one or more of voltage, current, temperature, SOC, SOH, and allowable charge/discharge current of the unit cell, a power line communication unit which performs wire communication, and a wireless communication unit which performs wireless communication, the information diagnosed by the abnormality diagnosis unit is output through the power line communication unit to the battery controller; and the information calculated by the state detection unit is output through the wireless communication unit to the battery controller.