In this research, we present a novel approach for actively balancing a Lithium battery string, modularized into numerous cells in a series configuration, called the multi-module balancer (MMB). The MMB is designed to balance the voltage among cells within each battery cell module and between the modules. To achieve high-speed balancing of voltage differences among cells in each module, an inner balancing circuit (IBC) for each battery cell module is utilized. The IBC utilizes a multi-winding transformer with forward conversion to effectively balance the voltage differences among cells in the battery cell module. For handling voltage differences between modules, an outer balancing circuit (OBC) based on a single switched capacitor is utilized. The OBC transfers energy from the battery cell module with the highest voltage to the one with the lowest voltage, detected by the MMB. To optimize energy conversion efficiency, the MMB minimizes energy loss by using fewer switches. Additionally, the proposed balancer offers the flexibility to expand the number of cell modules in series, as well as the number of cells in each module. This feature makes MMB suitable for high-power applications, including electric vehicles and power storage systems.