This paper presents a follow-up verification study on end-of-life lithium-ion cells from an electric ferry system, addressing both first-life and second-life utilization beyond state-of-health (SoH)-based criteria. In current practice, battery replacement decisions are commonly guided by SoH thresholds, typically in the range of 70-80%. However, such capacity-based criteria do not necessarily reflect economic viability under real operating conditions.

In this work, round-trip efficiency is evaluated under a ferry-representative operational profile and calculated as an average over three repeated cycles to improve robustness. The results are used to assess whether continued ferry operation remains economically meaningful, recognizing that efficiency degradation increases the required input energy even when cells remain above formal SoH limits.

For the second-life perspective, cell-level performance is evaluated using a set of short-term metrics, including efficiency under C/2 cycling, baseline low-rate performance, voltage behavior, and short-term self-discharge. Open-circuit voltage (OCV) retention over one week is used as an approximate indicator of short-term energy retention. In contrast to previous work focusing on cell-to-cell variability, the present study emphasizes cycle-to-cycle variation within individual cells to improve the reliability of performance assessment.

The study demonstrates that efficiency provides a complementary indicator to SoH for first-life decision-making, while a broader set of short-term performance metrics supports second-life suitability assessment, enabling a structured transition between applications.