In modern interrelated power systems, maintaining Load Frequency Control (LFC) is of paramount importance to ensure grid stability and reliable power supply. The Proportional-Integral (PI) controllers are widely used for LFC due to their simplicity and effectiveness. Conversely, the enactment of traditional PI controllers can be affected by varying system conditions and disturbances. To address this issue, this research proposes a novel approach to enhance LFC by employing dual-mode gain scheduling of PI controllers with Redox Flow Battery (RFB) integration, optimized using Particle Swarm Optimization (PSO). The dual-mode gain scheduling technique allows the PI controllers to dynamically adapt to different operating scenarios. By employing a two-mode switching mechanism, the controllers can select appropriate gains based on system conditions, enabling improved response and stability during varying load conditions and disturbances. Additionally, the integration of a redox flow battery provides an energy storage solution, allowing the system to respond more effectively to sudden load changes and grid imbalances. To optimize the performance of the dual-mode gain scheduling, the particle swarm optimization algorithm is utilized. PSO efficiently searches the parameter space, finding optimal gain values for the PI controllers, and thus, maximizing the overall LFC performance in the overlapped power system. The results exhibit the superiority of the dual-mode gain scheduling with RFB integration over traditional fixed-gain PI controllers. The system exhibits improved frequency regulation, reduced frequency deviations, and enhanced resilience to disturbances, showcasing the effectiveness of the proposed methodology.