To improve the state-of-charge (SOC) balancing ability and reduce the power loss, this paper proposes a discontinuous pulsewidth modulation (DPWM)-based battery power management method for cascaded H-bridge converter-based battery energy storage systems (CHB-BESS). First, two types of voltage-clamping principles are designed for each submodule (SM) of the CHB-BESS. Second, to address the limitations of conventional DPWM with fixed low power adjustment in CHB converter applications, the proposed method determines the maximum number of voltage-clamping SMs according to their SOC values and the output voltage references of the CHB-BESS. As a result, the SOC balancing ability can be fully exploited under both active and reactive power operation conditions, and the total power loss of the CHB-BESS can be substantially reduced. Finally, voltage-clamping SMs are selected according to their SOC sorting results, and the output voltage references of remaining non-voltage-clamping SMs are recalculated for modulation. Simulation and experimental results indicate that under varying active and reactive power operation conditions, the proposed method can improve the SOC balancing speed and reduce the power loss of the CHB-BESS.