Battery energy storage applied to power systems requires a large number of individual batteries to be connected in series and parallel, and connected to the grid through power electronic conversion circuits. Therefore, accurately grasping the characteristics of the battery and the needs of the grid, and optimizing the design, is the key to the battery energy storage system. This chapter mainly introduces the system composition, grid connection and operation control methods for lithium-ion batteries and lead-carbon batteries and other battery energy storage systems.