BATTERY ENERGY STORAGE SYSTEM

A battery energy storage system is provided with: a charging/discharging control device capable of controlling charging/discharging of each of a plurality of electricity storage units in accordance with the supply and demand state of a power system; and a management device for adjusting the progression of deterioration of each of the electricity storage units by differentiating the charging/discharging amount of each of the electricity storage units and managing by differentiating the electricity storage units having a low degree of progression of deterioration from the electricity storage units having a high degree of progression deterioration.