State of Health (Battery)
State of Health (SoH) is a measure of a battery's current capacity relative to its original capacity, expressed as a percentage. Under EU Regulation 2023/1542 (the Battery Regulation), State of Health is a mandatory data field in the Battery Passport for EV batteries and industrial batteries.
Full Definition
State of Health (SoH) is defined in EU Regulation 2023/1542 as "a measure of the general condition of a battery and its ability to deliver the specified performance compared with a new battery." It is typically expressed as a percentage — a battery with 80% SoH has 80% of its original capacity. SoH decreases over time due to charge/discharge cycling, temperature exposure, and other degradation mechanisms.
Under the Battery Regulation, the SoH data in the Battery Passport must be updated throughout the battery's lifetime. This is one of the most technically challenging aspects of Battery Passport compliance — the DPP must contain current SoH data, not just the SoH at the time of manufacture. This requires a connection between the battery management system (BMS) and the DPP registry, so that SoH data is automatically updated as the battery ages.
SoH data is critical for second-life applications — using EV batteries that have degraded below automotive performance thresholds (typically 80% SoH) in stationary energy storage applications. The Battery Passport's SoH data enables second-life operators to assess the remaining capacity of used batteries without disassembling them. This is expected to create a significant market for second-life battery applications as the first generation of EVs reaches end of automotive life.
Related Terms
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Register Your Digital Product Passport →State of Health: Definition and Measurement
State of Health (SoH) is a measure of a battery's current capacity relative to its original capacity. A new battery has a SoH of 100%. As the battery is charged and discharged, its capacity degrades — a battery with a SoH of 80% has 80% of its original capacity remaining. The EU Battery Regulation (EU 2023/1542) requires that the SoH of industrial batteries and EV batteries be disclosed in the Digital Battery Passport, and that the SoH be accessible via the battery's QR code or NFC tag. The SoH must be calculated using the methodology specified in the EU Battery Regulation's implementing acts, which are based on the IEC 62660-1 standard for lithium-ion batteries.
SoH Measurement Methods
There are several methods for measuring battery SoH: capacity measurement (measuring the actual capacity by fully charging and discharging the battery under controlled conditions), impedance spectroscopy (measuring the battery's internal impedance, which increases as the battery ages), and model-based estimation (using a mathematical model of the battery's degradation to estimate SoH from operational data such as voltage, current, and temperature). For the EU Battery Regulation's DPP requirements, the SoH must be measured using a standardised method specified in the implementing acts. Battery management systems (BMS) in EV batteries and industrial batteries typically include SoH estimation algorithms that can provide the SoH data needed for the DPP.
State of Health is a key parameter in the EU Battery Regulation (EU 2023/1542) DPP requirements for electric vehicle batteries and industrial batteries. The EU Battery Regulation requires that the SoH of EV batteries be disclosed in the battery DPP and that the SoH measurement methodology be standardised across all battery manufacturers. The EU Commission has mandated the development of a standardised SoH measurement methodology through the European standardisation organisations (CEN/CENELEC). The standardised SoH methodology will enable consumers and second-life battery operators to compare the SoH of batteries from different manufacturers on a consistent basis. Battery manufacturers should monitor the development of the standardised SoH methodology and ensure that their battery management systems are capable of measuring and reporting SoH in accordance with the standard.