Due to wind fluctuation and load disturbances，large scale energy storage system is required for maintaining power stability in a microgrid，especially with high penetration of wind power generation or no wind turbines during islanded mode.Huge battery energy storage system（BESS）is composed of lead-acid battery and power conditioning system（PCS）.It is integrated into the microgrid.The architecture of the BESS is proposed and a new control method is presented to enable linear/nonlinear load sharing by parallel connected BESS without communication among them.The feature of lead-acid battery is investigated and the operation of PCS is introduced as well.The effectiveness of the BESS and proposed control method is verified through simulations and experiments.