A Data-Driven Framework for Assessing Second-Life Electric Vehicle Batteries for Stationary Energy Storage Applications

The increasing adoption of electric vehicles (EVs) is expected to generate a substantial number of retired lithium-ion batteries, creating both environmental challenges and opportunities for second-life energy storage applications. However, the performance variability of retired batteries makes the identification of suitable candidates for repurposing a significant challenge. This study proposes a Battery Stability Index (BSI) framework for evaluating the suitability of second-life EV batteries for stationary energy storage applications supporting EV charging infrastructures. Battery cycling data from Nissan Leaf and Mitsubishi i-MiEV battery packs were analyzed using degradation rate, energy efficiency retention, operational stability, and energy throughput indicators. In addition, EV charging demand data were utilized to assess charging session support capability as a practical deployment-oriented performance metric. The proposed BSI integrates stability, degradation, and throughput characteristics into a unified assessment framework for battery ranking and suitability evaluation. The results demonstrate significant performance differences between the evaluated battery families. Nissan Leaf batteries exhibited lower capacity degradation rates (0.0086) than Mitsubishi i-MiEV batteries (0.0170), maintained higher energy efficiency retention (91.4% versus 79.0%), and achieved substantially greater energy throughput (21,911 Wh versus 6230 Wh). Furthermore, Nissan Leaf batteries supported up to 1.16 EV charging sessions, whereas Mitsubishi i-MiEV batteries supported fewer than 0.34 sessions. Consequently, Nissan Leaf batteries achieved the highest BSI values, with Leaf-1 and Leaf-2 obtaining scores of 0.658 and 0.638, respectively. The findings demonstrate that battery suitability cannot be reliably determined using a single health indicator. The proposed BSI framework provides a comprehensive and practical approach for identifying suitable second-life batteries, supporting battery repurposing decisions, sustainable energy storage deployment, and the integration of second-life batteries within EV charging ecosystems.