The Battery Energy Storage (BES) is expected to be a device supplying frequency control reserves in a power system penetrating large amount of Intermittent Renewable Energy Sources (IRES). The authors presented the Battery-Assisted Load Frequency Control (BALFC) as a novel BES utilization method contributing to enhance the LFC performance in previous works. In the BALFC, the BES compensates the slow responsivities of the LFC units by absorbing components of the LFC signal exceeding the maximum ramp rate of each unit. This paper proposes the Improved-BALFC in which the BES control signal is processed from the output signal of power plants including the control signal of Economic Load Dispatching (ELD) in addition to the LFC signal. A simulation study shows that the Improved-BALFC can suppress the frequency fluctuation larger than the BALFC when the load demand has long-period change.