Unlocking the value of retired EV batteries: Technologies, application, and commercial models for second-life energy storage in power systems

The large-scale retirement of electric vehicle (EV) batteries presents a dual challenge: managing end-of-life systems while harnessing residual value to enhance power system sustainability. Owing to the relatively modest performance requirements of stationary applications, repurposing retired EV batteries as second-life battery energy storage systems (SL-BESSs) provides a cost-effective means to extend service life and improve resource efficiency. This review systematically evaluates the technical, operational, and institutional foundations required for the effective integration of SL-BESSs into power systems. In this context, echelon utilization is positioned as a pivotal transitional stage toward a circular battery economy. Building on this perspective and moving beyond prior studies that focus on reuse feasibility or single-case assessments, this work synthesizes three core dimensions: battery management algorithm adaptation, scenario-driven deployment compatibility, and scalable commercial model architectures. Key technical obstacles are identified, including cell-level inconsistency, limited operational data, and uncertainty in degradation forecasting. Mitigation strategies are discussed, referencing advances in clustering algorithms, transfer learning, and hybrid physical-data modeling. Deployment suitability is assessed across generation, grid, and end-user segments based on application-specific requirements and evidence from global demonstration projects. A structured classification of commercial models, including Battery-as-a-Product, Battery-as-a-Service, Platform-as-a-Service, and Energy-as-a-Service, is presented and linked to policy frameworks and performance benchmarks. This alignment informs the development of scalable deployment pathways. By integrating perspectives from control engineering, systems integration, and market design, this review provides a robust analytical foundation for advancing second-life battery applications in power systems. Although interest in this area is growing, comprehensive interdisciplinary research and collaboration remain necessary.