In the hybrid energy storage system (HESS), the voltages between the battery cell and the supercapacitor cell are different, increasing the circuit and control complexity of the balance system. Therefore, a bidirectional integrated equalizer based on the Sepic–Zeta converter is proposed for the HESS, which realizes both battery string and supercapacitor string balance during the energy exchange. The inductors in the Sepic–Zeta converter are used as the primary side of the balanced multiwinding transformer. The Sepic–Zeta converter generates the current ripples to drive the multiwinding transformer. The secondary side generates currents to balance the HESS, and hence, the equalizer itself is essentially switchless. Therefore, the proposed circuit can reduce the complexity of the HESS. Experimental and comparative results show that the proposed equalizer achieves the balance of the HESS.