PassPer / Resources / State of health in the battery passport
Battery passport guide

The one field in the passport that refuses to sit still.

Most of a battery passport is written once: chemistry, carbon footprint, due diligence — facts fixed at manufacture. State of health is different. It changes with every year of service, and the passport is required to keep up. From 18 February 2027, that turns the battery passport from a birth certificate into a living record — and raises a hard operational question: who may update it, and how is that controlled?

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In one line: state of health is the dynamic heart of the battery passport — current versus rated capacity, updated only by authorised operators, with an audit trail — and the documented SoH history is what gives a used battery a verifiable price.

Static birth certificate, dynamic health record

The battery passport mandated by Regulation (EU) 2023/1542 — required from 18 February 2027 for every EV battery, every LMT battery and industrial batteries above 2 kWh — carries over a hundred data points. Most are static: cell chemistry, material origins, carbon footprint, due diligence. They describe the battery as it left the factory and never change.

Performance and durability data breaks that pattern. State of health — in essence, how much of the battery's rated capacity remains available today — is only meaningful if it is current. A five-year-old passport showing factory-fresh capacity is not merely stale; it is wrong, and misleading to every downstream reader from buyers to recyclers. The regulation therefore treats the passport as a record to be kept up to date across the battery's life, not filed once and forgotten.

Rated versus current: the number that sets the price

SoH is usually expressed against the baseline set at manufacture: rated capacity, versus the capacity the pack actually delivers now. That single ratio drives most of the commercial decisions made about a used battery:

Who may hold the pen

A record that changes needs rules about who changes it. The framework's answer is authorisation: dynamic passport fields are written by the responsible economic operator and by operators authorised to update battery data — think qualified repairers, remanufacturers and second-life operators — rather than by anyone who scans the code. The exact roles and their permissions are defined by the regulation and its implementing rules, so the honest summary is: writing is a privilege attached to a regulation-defined role, and any serious passport platform enforces that rather than inventing its own scheme.

The corollary matters as much as the rule: every update must be attributable. An SoH figure is only worth what its provenance is worth — who measured it, when, in what role.

What a passport platform has to do about it

Handling dynamic data cleanly is a systems problem, and it is where passport platforms earn their keep. The ingredients: role-based write access, so only authorised actors can touch dynamic fields; versioning, so the passport shows current SoH without erasing history; an immutable audit trail recording every change with author and timestamp; and longevity, because the record must stay accessible for the battery's regulated lifetime. PassPer builds passports this way from the start — eIDAS-seal-ready (QTSP onboarding in its final stage), served via GS1 Digital Link QR, with authorised-update flows and a complete change log — so the passport you register for 18 February 2027 is still trustworthy when the pack starts its second life. See where you stand with the free readiness check.

Frequently asked questions

What exactly is state of health?
State of health (SoH) expresses the current condition of a battery relative to its condition when new — most intuitively, remaining capacity as a share of rated capacity. A pack rated at 60 kWh that now holds 48 kWh is at roughly 80% SoH. The battery passport framework treats it as part of the performance and durability data the passport must carry and keep current.
Who is allowed to update the state of health in a passport?
Not anyone with the QR code. The regulation foresees updates by authorised actors — the responsible economic operator and operators authorised to act on battery data, such as qualified repair, remanufacturing or second-life operators. The precise roles are defined by the regulation and its implementing rules, so treat any platform's role list as an implementation of those rules, not a substitute for them.
Does the passport need a live telemetry feed from the battery?
No. The passport is a structured record of defined data points, not a real-time stream. SoH values enter it through authorised updates — for example after a diagnostic test or service event. Guidance such as DIN DKE SPEC 99100 helps define how performance and durability data should be structured and maintained.
What happens to the passport when a battery gets a second life?
The record follows the battery. A change of status — say, an EV pack repurposed for stationary storage — is exactly the kind of lifecycle event the passport is designed to capture, and the documented SoH history is what makes the repurposed pack sellable: the buyer can see rated capacity, current capacity and who verified it, instead of taking the seller's word.
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