What really matters in Battery State of Health (SoH) Testing? 

We interviewed Dr. Gael Chouchelamane, a former JLR battery engineer and one of our independent experts at Electrification Academy, to share insights about what really matters in battery state of health (SoH) testing.

Battery SoH testing procedures and outcomes play an important through the entire battery lifecycle from battery cell, module and pack design through to warranty decisions, recycling and second life evaluations.

As the secondary market for used batteries expands, battery state of health testing becomes an important part of battery safety for dismantlers, recyclers, and secondary battery users.  

In this interview we ask Dr. Chouchelamane these questions about battery SoH Testing, and what advice he has for battery teams: 

1. What was your role when you worked with lithium-ion battery SOH testing? 
2. What specific tasks or responsibilities did you have related to SOH testing? 
3. How did you conduct or oversee SOH testing, and why did you choose that approach? 
4. In your experience, what was the biggest challenge you faced during SOH testing? 
5. How did your SOH testing work influence battery design, diagnostics, warranty decisions, or second-life evaluations? 
6. Looking back, what advice would you give to teams currently developing or improving their SOH testing processes? 

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Throughout my career I’ve been responsible for the technical validation, aging assessment and lifecycle evaluation of Li-ion battery systems in automotive, marine and stationary applications.

My roles ranged from HV battery systems technical expert to Chief engineer and later independent consultant.

Battery SOH testing was central to my work whether supporting warranty models, developing design-of-experiment aging campaigns or building complete second-life testing ecosystems.

My responsibilities have covered the full chain of SOH-related activities, including:

• Designing Design of Experiments for aging and warranty models
• Developing battery test jigs, fixtures and controlled laboratory conditions that accurately reflect real-world usage fro SOH testing
• Authoring detailed test protocols covering cycling, rest periods, characterization and pass/fail criteria
• Building data-processing tools to extract and analyze capacity fade, resistance growth and pulse-power capability
• Leading battery grading frameworks for second-life applications, aligned with industry standards
• Training technicians, defining workflow layouts and creating safe module-handling and pack-removal processes
• Supporting clients in establishing end-to-end ecosystems, from identifying suitable donor vehicles through to module-level SOH testing and repurposing

I took a structured and realistic approach, combining controlled laboratory testing with usage-based conditions.

In 2015, for warranty aging work, I developed laboratory test conditions that closely replicated real-world vehicle behavior, matching load profiles, temperatures and cycling patterns. This meant designing a comprehensive DoE, building custom jigs and standardizing the characterization routines.

More recently, in second-life applications, I used a multi-stage approach:

• Safety and initial characterization (insulation, voltage checks, basic capacity and impedance)
• Detailed electrical testing aligned with the latest industry standards for repurposing
• Grading and traceability, ensuring results are reliable and repeatable across technicians and sites

This blended approach ensured that SOH results were both technically accurate and operationally meaningful.

The biggest challenge has consistently been replicating real-world conditions accurately whether for aging prediction, warranty modeling or second-life assessment. Real usage is highly variable, and incomplete or inconsistent historical data can distort SOH results.

On the second-life side, the main challenge is variability and provenance. Incoming used packs rarely come with complete histories, making consistent grading difficult unless strict, standardized test protocols are applied. However there are now tools that exist that can help grade batteries in a matter of a few minutes once calibrated.

The key lesson is that SOH is not a single number.

Capacity or impedance alone never tells the full story. True SOH assessment combines safety, electrical performance, thermal behavior and historical usage patterns analysis.

Mechanical testing is still the missing piece though.

Some startups have developed tools to “look inside” the battery without opening it, but I haven’t tested these solutions myself, so I can’t comment on their accuracy. If proven reliable however, they could enable a truly robust second-life testing protocol.

Another important lesson is the value of standardization and technician training. Even with perfect test protocols, results can vary significantly if technicians, workflows or equipment setups differ. Creating repeatable processes is just as important as designing the tests themselves.

My SOH work has had several direct impacts:

• Warranty and aging models: Usage-based testing improved the accuracy of warranty degradation predictions and helped OEMs set thresholds grounded in real behavior.
• Design decisions: Aging data fed back into thermal management strategies, BMS algorithms and cell selection
• Diagnostics: Insights from characterization tests contributed to improved BMS SOH estimation and anomaly detection
• Second-life operations: My recent work created a full ecosystem, sourcing, disassembly, testing and grading which led to a structured, standards-compliant second-life operation capable of safe and predictable repurposing

• Prioritize realism. Align test conditions as closely as possible with real usage—otherwise results won’t translate to the field.
• Standardize everything. Protocols, fixtures, pass/fail criteria, technician training. Consistency is key to reliable SOH assessment
• Use multiple indicators. Capacity fade alone is insufficient; combine electrical, thermal and safety metrics.
• Ensure good provenance control. Especially for second-life applications, traceability is essential.
• Think end-to-end. SOH testing doesn't exist in isolation, it affects design, warranty, repurposing and operational safety.

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