Batteries play a central role in the global energy transition. They power electric vehicles, support renewable energy systems and serve several industrial functions. With the rising demand for EVs and energy storage systems, understanding how long they will perform reliably becomes increasingly important.
Battery State of Health (SoH) is the measurement of this understanding. Without accurate SoH assessment, decision-making about battery use, safety, second-life opportunities and end-of-life treatment becomes limited and uncertain.
Today, we’ll explore why SoH is a critical indicator, how Digital Battery Passports (DBPs) help measure it more accurately, and why this advancement is important for manufacturers, reuse operators, regulators, and the circular battery economy.
What Is Battery State of Health?
Battery State of Health describes the current condition of a battery relative to its condition when it was new. It is usually expressed as a percentage. A battery with 100 per cent SoH is performing at the level it was designed for at the time of manufacture, while lower percentages indicate how much performance and capacity have been lost through use and ageing.
Over time, as a battery undergoes repeated charging and discharging and exposure to environmental stressors, SoH typically declines. A battery with a high SoH retains more of its original capacity and performance than one with a low SoH.
Accurate SoH measurement informs expectations about remaining useful life and supports decisions on repair, reuse, repurposing and recycling. For example, a battery that retains 80 per cent of its original capacity might no longer meet the performance demands of an electric vehicle but could still be viable for homes or grid-scale energy storage.
Why Accurate State-of-Health (SoH) Measurement Matters
Accurate State-of-Health (SoH) data is essential for multiple stakeholders across the battery value chain.
Safety and performance assurance rely on understanding whether a battery can operate reliably in a given application. Reuse operators, such as second-life EV battery companies, need this information to determine whether a given battery is suitable for a second-life application. SoH has a significant influence on value assessment in second-life markets, informing pricing and investment decisions. Lifecycle planning depends on SoH data to identify when a battery should be repaired, repurposed, reused or recycled.
In all these areas, reliable SoH measurement supports better economic and sustainability outcomes.
Without good SoH data, organisations often face uncertainty. Traditional battery management systems and diagnostic tests can provide useful information, but they vary widely between manufacturers and lack standardisation. This makes it difficult to compare batteries or assess their suitability for second-life uses.
Challenges in Measuring Battery State of Health
There is no universal method for measuring SoH. Battery ageing affects not just capacity but also internal resistance, energy efficiency and the ability to deliver power reliably. Different conditions of use, temperatures and charging patterns all influence SoH differently.
In practice, battery management systems combine a range of measurements and models to estimate SoH. These may include analysing charge and discharge behaviour, voltage and current profiles, temperature effects and historical usage patterns. Some advanced approaches apply machine learning and statistical models to predict ageing based on real-world data. However, such methods must be tailored for different battery chemistries and use cases.
A consequence of this diversity is that SoH data has historically been fragmented, vendor-specific and difficult to share across stakeholders in a battery’s lifecycle.
How Digital Battery Passports Improve SoH Measurement
Digital Battery Passports represent a major shift in how battery information is recorded, shared and used. A DBP is a digital record that stores product-specific data throughout a battery’s life. This includes manufacturing details, materials, performance history, degradation metrics and traceability from production to end of life.
Under Regulation (EU) 2023/1542, battery passports are mandated and must include information on SoH and other performance indicators for electric vehicle batteries, industrial batteries and light mobility batteries above 2 kWh.
By storing SoH data consistently and digitally, DBPs overcome fragmentation and ensure that all relevant stakeholders have access to up-to-date, trusted information. Passports can include periodic updates on SoH based on Battery Management System (BMS) outputs and diagnostic tests, making it easier to track how a battery’s health evolves. A verified history of SoH helps reduce duplication of expensive independent testing, lowering cost barriers to second-life applications and improving market confidence.
The Link Between SoH, Market Trust and Circularity
Better SoH measurement supports the development of second-life battery markets by enhancing transparency and trust. Investors, energy project developers and second-life businesses require reliable data to evaluate risk and reward. Without robust SoH information, uncertainty limits reuse projects and slows circular economy progress.
Accurate SoH tracking also supports efficient use of resources. Batteries that might otherwise be discarded prematurely can continue in productive use, reducing resource extraction and energy usage associated with manufacturing new batteries. Digital Battery Passports help connect SoH data with reuse and recycling processes, enabling circular battery economy outcomes such as reduced waste and improved material recovery.
Academic research shows that battery passports, including accurate SoH data, can extend repurposed battery lifetimes significantly by tracking energy, power and efficiency metrics over extended periods. Some studies indicate that with appropriate SoH tracking, repurposed batteries could have an extended life of over a decade in suitable applications.
How BASE uses Digital Battery Passports to Improve SoH Insight
At the BASE project, we consider Digital Battery Passports to be fundamental for reliable SoH information. BASE is developing a passport framework that integrates performance data and historical records throughout a battery’s life. Our platform ensures that high-quality SoH data is captured, authenticated and updated as the battery moves through different stages of its lifecycle. This enables manufacturers, reuse operators, regulators and owners to make well-informed decisions about battery deployment, reuse suitability and end-of-life treatment.
Through pilot programmes involving real batteries across different use contexts, BASE is demonstrating how SoH data within a Digital Battery Passport enhances transparency, supports safer second-life deployment and strengthens circular battery use in Europe. These pilots help refine the methodologies we deploy and ensure alignment with evolving regulatory and market needs.
Closing Thoughts
As battery deployment continues to expand worldwide, the importance of accurate performance and health data will only increase. Digital Battery Passports will transform how SoH is measured, shared and acted upon. They create a reliable foundation for industry stakeholders, regulators and circular economy actors to make informed decisions throughout a battery’s life.
By improving transparency and trust, DBPs contribute to the development of a more sustainable and resilient battery ecosystem in Europe and beyond.
The BASE project has received funding from the Horizon Europe Framework Programme (HORIZON) Research and Innovation Actions under grant agreement No. 101157200.
References
Regulation (EU) 2023/1542 on batteries outlining passport requirements, including SoH data: https://t.ly/LN9di
MDPI - State of Health (SOH) Estimation of Lithium-Ion Batteries Based on ABC-BiGRU: https://www.mdpi.com/2079-9292/13/9/1675
BASE Project - Digital Battery Passport traceability and performance data: https://base-batterypassport.com/blog/traceability-9/digital-battery-passport-enabling-battery-lifecycle-traceability-from-mining-to-recycling-73
BASE Project - Six pillars of Digital Battery Passport including performance and SoH: https://www.base-batterypassport.com/blog/circularity-8/the-six-pillars-of-digital-battery-passport-content-how-base-project-strengthens-trust-transparency-and-circularity-65
MDPI - Battery Passport and Online Diagnostics for Lithium-Ion Batteries: A Technical Review of Materials–Diagnostics Interactions and Online EIS: https://www.mdpi.com/2313-0105/11/12/442