The rapid deployment of electric buses (EBs) presents a dual challenge to both the stability of the power grid and the resource utilization of retired batteries. Efficiently repurposing retired batteries with high energy storage potential has become a critical issue for advancing the circular economy and achieving the “dual carbon” targets. This study proposes an echelon utilization strategy for retired EB batteries in energy storage systems (ESSs) and develops a multi-model framework that integrates vehicle behavior simulation, battery degradation modeling, and retired battery flow prediction to quantify the available capacity of retired batteries in energy storage scenarios. By simulating battery performance under typical operating conditions, the integrated model can accurately predict the lifespan and remaining capacity and assess the storage potential of retired batteries. Results show that by 2040, the annual available energy storage capacity of retired batteries from Wenzhou’s EB fleets is expected to exceed 0.9 GWh, demonstrating high regional application potential and provides a new power source for achieving the “dual carbon” targets and sustainable development.