A battery energy storage system (BES) can provide fast active power compensation and hence it also can be used to improve the performance of the load frequency control. In this paper, the study is carried out on a single area model representing the whole power system considering generation rate constraint (GRC). An incremental model of BES is proposed and merged into the load frequency control of the power system. Optimum value of integral gain setting is obtained using integral squared technique (ISE). Dynamic responses of the system are presented with and without considering BES facility. Analysis reveals that BES improves the system performance significantly.