Recently, with the increasing prominence of electric vehicles and renewable energy, the demand for secondary batteries, which serve as energy storage devices, has also risen. To maintain battery efficiency and prevent performance degradation, various battery balancing techniques have been proposed. However, these existing techniques face technical limitations when the number of batteries is significantly expanded. To address these issues, this paper proposes a new battery balancing topology using a voltage-sharing method for modular batteries. The proposed topology is based on the principle of balancing battery voltages by sharing voltage through a single transformer that connects multiple battery modules in a flux-sharing active topology, ensuring that voltages converge to the same value. The characteristics of the proposed circuit were analyzed using PSIM simulations, and the results were verified through experiments.