High-capacity batteries connected in series and/or parallel in the battery energy storage system (BESS) and electric vehicle (EV) require cell balancing circuits to ensure their lifetime and safety. This paper proposes a variable capacitor model to simplify the SOC-OCV curve for rapid evaluation of the balancing time. Compared to the conventional variable voltage-source model, it can provide a rapid estimation of the balancing time with high accuracy by simple calculation of the R-C time constant based on the concept of charge-equivalent capacitance. The proposed method is useful for active balancing circuits as well as passive balancing schemes. Furthermore, the amount of change in the battery charge can be provided by the charge-equivalent capacitance, enabling the determination of battery SOC without the battery current information. After validating the model accuracy by experimental results, a switched-capacitor active balancing circuit is implemented to verify the effectiveness of the proposed model.