Performance Evaluation of Second-Life EV Batteries for Off-Grid Solar Energy Storage System

The increasing adoption of electric vehicles (EVs) has led to a growing volume of retired lithium-ion batteries that retain significant residual capacity, prompting interest in their repurposing for stationary energy storage systems (ESS). This study presents a comprehensive performance evaluation of second-life EV batteries sourced from three platforms: Nissan Leaf Gen 1 (LMO-LNO chemistry), Citroën C0 (Mitsubishi i-MiEV) (LMO), and China Aviation Lithium Battery Co., Ltd. (CALB) (LFP). Laboratory tests were conducted using Arbin battery testers to assess capacity retention, internal resistance, and state-of-health (SOH) across up to 5000 charge-discharge cycles. In parallel, real-world field tests were conducted using a solar-powered 120 W LED streetlight ESS to validate operational performance under ambient Malaysian climate conditions. Results from laboratory analysis showed that the CALB LFP battery exhibited the highest mid-life stability, retaining 70.9% of its capacity at 2500 cycles and 57.4% at 3000 cycles, with slower thermal-induced degradation. The Nissan Leaf battery maintained 72.6% capacity at 2500 cycles but experienced accelerated decay post-3000 cycles, dropping to 4.8% at 5000 cycles. The Citroën C0 battery showed comparable early-cycle behavior but degraded more sharply under thermal stress, retaining 63.6% at 3000 cycles and just 7.2% at 5000 cycles. Field test data revealed that actual SOH decline rates were 15–20% faster than in lab conditions, attributed to variable temperatures (30–38°C), inconsistent load patterns, and limited thermal management. The study confirms that second-life batteries are viable for low- to medium-demand ESS applications within a 2500–3000 cycle operating window, provided that chemistry-specific integration strategies and intelligent battery management systems are employed. The findings contribute to lifecycle extension modeling and support the deployment of second-life batteries as cost-effective, sustainable components in decentralized energy systems.