Experimental Assessments of Second-Hand Battery Degradation under V2G Operation for Electric Vessels

Vessel-to-Grid (V2G) technology offers significant potential for supporting grid stability, boosting renewable energy integration, and increasing the profitability of electric vessels (EVs) through intelligent energy management. However, concerns linger regarding the impact of frequent charge-discharge cycles on battery health, especially with the further inclusion of the V2G power cycles. The impact of this approach has been well-studied for road-based electric vehicles, where the concluded outcomes are particularly customised based on the road vehicle operational duty cycles. However, this approach remains largely unexplored for marine EV batteries, due to their unique duty cycles and implementation of second-hand battery systems for use in V2G technologies. This paper addresses that gap by investigating the impact of V2G on commercial lithium-ion battery packs (6.8 kWh, 44V, 12 cells) used in small-power leisure and light-duty marine vessels. A dedicated testbed was developed, incorporating a bidirectional DC power supply and integrated battery management system. Simulated operational cycles were applied to assess V2G use cases such as peak shaving, renewable energy integration, and energy trading. Accelerated cycling tests replicated real-world V2G patterns over several weeks, allowing for continuous monitoring of the battery state of health (SOH). Results show that while V2G is technically viable and economically beneficial for marine EVs, its effects on battery SOH, especially for second-life batteries, must be carefully managed to ensure long-term sustainability.