Patent attributes
An energy storage system including battery packs having a first terminal electrically connected to a first node and a second terminal electrically connected to a second node and configured to receive power from an external device or configured to provide power to the external device through the first and second nodes and a battery management system controlling the battery packs. Each battery pack includes batteries and a transistor unit electrically coupled between the batteries and the first node. The battery management system includes a measuring unit for measuring a state of charge (SOC) of the batteries of each battery pack, and a controller configured to calculate a high value, a low value, an average value, and a difference value between the high and low values from the measured SOCs, and configured to control the transistor units of the battery packs, based on the calculated high, low, average, and difference values.