The reuse of batteries after their initial service life in electric vehicles or other high-demand applications presents a significant opportunity for sustainability and cost reduction. However, the absence of standardized performance metrics for second-life batteries introduces complexities for manufacturers, recyclers, and end-users. The challenges span testing protocols, state of health estimation, and certification, creating barriers to widespread adoption.
One of the primary obstacles is the lack of uniform testing protocols. Second-life batteries originate from diverse sources, with varying usage histories, chemistries, and degradation patterns. Without consistent methodologies to evaluate remaining capacity, cycle life, or safety, comparisons between different batches become unreliable. Some manufacturers employ proprietary testing routines, while others rely on ad-hoc assessments, leading to inconsistencies in performance claims. For instance, a battery graded as suitable for stationary storage by one entity might fail to meet another’s criteria due to differing discharge rates or temperature conditions during evaluation. This variability complicates procurement decisions for potential buyers, who cannot confidently assess quality or longevity.
State of health estimation further complicates standardization. SOH is a critical metric indicating a battery’s remaining useful life, typically expressed as a percentage of its original capacity. However, multiple methods exist to calculate SOH, including capacity-based, impedance-based, and model-based approaches. Each technique has limitations—capacity testing is time-consuming, impedance measurements may not correlate directly with aging mechanisms, and model accuracy depends on input data quality. Discrepancies arise when different stakeholders apply distinct SOH methodologies, resulting in conflicting assessments of the same battery pack. For example, a recycler might report an 80% SOH using impedance measurements, while an end-user observes only 70% capacity retention under real-world conditions. Such mismatches undermine trust in second-life battery performance claims.
Certification standards for second-life batteries remain underdeveloped compared to those for new batteries. Organizations like UL and IEC have established safety and performance benchmarks for primary battery systems, but equivalent frameworks for reused batteries are scarce. The absence of universally recognized certification processes means that second-life batteries often enter markets without rigorous validation, increasing risks for adopters. Some regions have begun addressing this gap—for instance, the European Union’s Battery Directive includes provisions for repurposed batteries, but enforcement mechanisms are still evolving. Without clear regulatory guidance, manufacturers hesitate to invest in second-life systems, fearing liability or reputational damage if reused cells underperform or fail prematurely.
Industry consortia and governments are working to establish guidelines, though progress is incremental. The Global Battery Alliance has outlined principles for sustainable battery reuse, emphasizing traceability and transparency in performance reporting. Similarly, the California Energy Commission has funded research into second-life battery testing frameworks, aiming to develop reproducible metrics. These efforts, however, face challenges in reconciling stakeholder priorities. Battery manufacturers prioritize safety and liability mitigation, recyclers focus on cost-effective recovery processes, and end-users demand reliable performance data. Aligning these interests requires collaboration, yet competing commercial agendas often slow consensus-building.
Battery manufacturers advocate for conservative SOH thresholds to minimize warranty risks, while recyclers push for more lenient criteria to maximize the volume of reusable cells. End-users, particularly in cost-sensitive applications, seek affordable solutions but lack tools to verify vendor claims independently. This tension highlights the need for neutral, science-based standards that balance safety, economics, and performance. Pilot programs, such as those by automakers to redeploy used EV batteries in energy storage, provide valuable data but are not yet scalable due to small sample sizes and controlled conditions.
Recyclers face additional hurdles in standardizing second-life battery evaluation. The process of sorting, testing, and repurposing used batteries is labor-intensive and requires specialized equipment. Without standardized metrics, recyclers must develop in-house testing procedures, increasing operational costs. Some companies have adopted machine learning algorithms to predict battery health from partial data, but these tools require validation across diverse battery types and usage scenarios. The lack of shared datasets or benchmarking platforms further impedes progress, as recyclers cannot compare their methods against industry norms.
End-users, meanwhile, struggle with uncertainty over second-life battery performance. Unlike new batteries, which come with standardized warranties and performance guarantees, reused batteries often have limited or inconsistent assurances. This uncertainty discourages adoption, particularly in applications where reliability is critical. Even when performance data is available, the absence of standardized reporting formats makes it difficult for buyers to compare options across suppliers.
Efforts to harmonize standards are gaining momentum but require sustained investment. Cross-industry initiatives, such as the Second Life Battery Consortium, aim to bridge gaps by developing common testing protocols and certification pathways. Governments can accelerate progress by funding research and mandating transparency in second-life battery transactions. For example, requiring sellers to disclose testing methodologies and historical usage data would empower buyers to make informed decisions.
The path toward standardized metrics for second-life batteries is fraught with technical and logistical challenges, but the potential benefits justify the effort. Uniform testing protocols, reliable SOH estimation methods, and robust certification standards would unlock broader market acceptance, driving the circular economy for energy storage. Until then, stakeholders must navigate a fragmented landscape, balancing innovation with the need for credibility and safety.
The evolution of second-life battery standards will depend on collaboration across the value chain. Manufacturers, recyclers, and end-users must align on shared goals, while policymakers provide the framework for accountability. Only through coordinated action can the industry overcome the current ambiguities and establish a trustworthy foundation for second-life battery deployment.