energy · transport · circular-economy · family: the missing yardstick
a passport with an unmeasured vital sign
The EU battery passport becomes mandatory on 18 February 2027 and must carry a battery's state of health — but no standard way to measure state of health at the vehicle level exists, and the only number available comes from the manufacturer's own software
Problem statement
Under Regulation (EU) 2023/1542, every electric-vehicle and light-means-of-transport battery, and every industrial battery above 2 kWh, placed on the EU market from 18 February 2027 must carry a digital battery passport, whose contents include "performance and durability data" and information supporting repair, reuse and recycling; the Commission's timeline for the passport lists, for July 2026, an implementing decision on the adoption of six of the eight harmonised standards developed by CEN-CENELEC JTC 24, and describes its dates as indicative. Yet the single number that second-life buyers, insurers, recyclers and used-car purchasers most want from that passport — the battery's state of health (SoH) — has no agreed measurement basis. A 2025 analysis from TU Munich's automotive-technology institute states that "neither industry nor academia has a consensus on a vehicle-level SOH definition or a standard procedure for its measurement," that the regulation's SoH articles "lack technical detail and merely state that it must be given as an energy-based value for electric vehicles, named the state of certified energy (SOCE)," and that "the regulation misses a definition of standard measurement and reference for obtaining the SOH or SOCE, which substantially impacts the values obtained." The number a vehicle reports today "is supplied by the original equipment manufacturer (OEM), which can have an incentive to manipulation so that it does not necessarily coincide with actual battery aging." The unsolved problem is a reproducible, scalable, manipulation-resistant vehicle-level SoH measurement that can be written into a passport before the passport becomes mandatory.
Why this matters
SoH is the value on which an EV's residual value, warranty disputes, insurance premiums, and its routing into reuse versus recycling all turn — the paper notes it "lays the foundation for assessing the residual value of secondhand vehicles" and that stakeholders need it "to operate the battery within ideal parameters and make informed decisions regarding maintenance, use in second-life applications, or recycling." A passport that carries an OEM-estimated SoH with no common reference invites exactly the cross-manufacturer incomparability that the passport was created to remove: two cars reporting "90 percent" may have degraded by different amounts, through different mechanisms, measured by different algorithms. The regulatory clock makes this a window rather than a research curiosity: the passport date is fixed, the JTC 24 standards are being adopted now, and the paper reports that the Battery Pass consortium — a publicly funded initiative — has already criticised the lack of regulatory clarity.
What’s been tried and why it hasn’t worked
The regulatory and standards landscape has produced pieces that do not fit together. UN Global Technical Regulation No. 22 (incorporated in Euro 7) is, per the authors, the only instrument that "addresses the necessity and challenges for vehicle-level health metrics," but it verifies durability through the WLTC driving cycle, "through which the SOCE and state of certified range (SOCR) are determined, but not the remaining capacity, which is, however, necessary for the previously mentioned EU regulation"; ISO 12405-4 "vaguely proposes standard (dis)charging cycles for battery packs of EVs relying on the battery 'supplier's recommendations,' which are not publicly available." Technically, model-based SoH estimation (electrochemical or equivalent-circuit models running in the BMS) "inherit[s] model inaccuracies and [is] either unsuitable for online application or imprecise" and is OEM-controlled; measurement-based alternatives each fail a criterion — chassis-dynamometer driving cycles are reproducible "but is cumbersome, time-consuming, and expensive, impairing scalability," on-road profiles are "not reproducible due to fluctuating external influences," continuous discharge through auxiliaries wastes energy, and bidirectional charging "has yet to be widely adopted." A practical obstacle the authors flag: pack voltage, the quantity a reproducible protocol should be defined on, "is less accessible and currently must be reverse-engineered from controller area network (CAN) data so that simple access to the voltage must be granted, e.g., through the onboard diagnosis (OBD)-II interface." So the field has a mandated metric, competing partial procedures, and no public, vehicle-agnostic reference.
What would unlock progress
The authors' proposal is a concrete candidate for the standard: use ordinary onboard charging (which happens anyway and follows standardised protocols such as ISO 15118 / IEC 61851) as the controlled stress, at a constant power low enough to be reproducible (they derive a maximum of about 8 kW for a 120 kWh pack, below a typical 11 kW EU wallbox), over a fixed pack-voltage window "declared in the vehicle's registration documents," after a rest period (a 30-minute rest sufficed in their study), at room temperature, with differential-voltage analysis to attribute the loss to aging mechanisms — measurable charger-side on DC chargers via ISO 15118 data. What would unlock adoption is independent replication across many vehicle makes, an agreed public voltage-window and rest-period specification, regulatory access rights to pack voltage via OBD-II, and a mapping from the resulting capacity- and energy-based SoH to the regulation's SOCE so that JTC 24 or a delegated act can reference it.
Entry points for student teams
A team with access to one or more EVs and a wallbox could prototype the charging-based SoH measurement: log CAN/OBD-II pack voltage and current during controlled constant-power charges over a fixed voltage window, compute capacity- and energy-based SoH with differential-voltage analysis, repeat to quantify reproducibility, and compare against the BMS-reported SoH — publishing the protocol and data openly. A standards-oriented team could draft the specification text (voltage window declaration, rest, temperature, charge power, data fields) in the JTC 24 / Annex XIII data-model format and test it against second-life buyers' and insurers' needs. A data team could analyse existing open EV telemetry to estimate how far OEM-reported SoH diverges across brands for similar mileage and age. Relevant skills: electrical/battery engineering, vehicle CAN diagnostics, standards writing, data analysis.
Genes
Structural cousins: stuck the same way, in other fields
Sources
Bilfinger P., Schreiber M., Rosner P., Abo Gamra K., Schöberl J., Grosu C., Lienkamp M. (Technical University of Munich), "Why we need a standardized state of health measurement procedure for electric vehicle battery packs — a proposal for energy- and capacity-based metrics," npj Clean Energy 1:10, published 10 October 2025 (open access), accessed 2026-08-18; European Commission, "Batteries — Digital Product Passport" (timeline page), accessed 2026-08-18 go to source 1 ↗ go to source 2 ↗
Working notes
Notes made while writing and checking this brief, shown as written. They use working shorthand.
All quotations about the SoH gap, GTR 22, ISO 12405-4, OEM incentives, measurement approaches, the ~8 kW / 120 kWh derivation, the 30-minute rest, and OBD-II access are from the full open-access text of Bilfinger et al. 2025 (npj Clean Energy 1:10, TUM) retrieved on 2026-08-18; the paper carries an author correction dated 31 December 2025 (checked at verification 2026-08-18: it corrects only the article title, from "definition" to "measurement procedure"; no data or quotations affected). The passport date (18 February 2027), covered battery categories, data-content headings, and the July 2026 implementing decision adopting six of eight JTC 24 standards are from the European Commission's Batteries DPP timeline page read on 2026-08-18. Which delegated/implementing acts on state-of-health parameters (Regulation Annex VII / Article 14) remain outstanding as of August 2026 was not established from a primary source this session — flag for verification against EUR-Lex. `temporal:window` is a deadline window (mandatory passport date; standards under adoption now). `failure:regulatory-mismatch` is the "wrong measurement basis" sub-pattern: the regulation mandates a metric without a measurement definition. `constraint:coordination` was considered and rejected on filter (2): the binding constraint is the absence of a defined, reproducible measurement (data/regulatory), not unwilling actors. `stakeholders:multi-institution` passes: OEMs hold the BMS data and vehicle access, the Commission/CEN-CENELEC/UNECE hold the standards, and second-life, insurance and recycling actors hold the use cases; no single actor can define and enforce the metric alone. Related collection briefs: `energy-ev-battery-cold-climate-performance` (battery performance, not measurement) and `circular-recycled-plastics-pcr-spec-void` (a parallel "no one can specify the metric" problem in a different material stream); no existing brief covers battery-passport or SoH measurement.
Source type: Self-articulated (academic battery-research group and the EU regulator's own timeline)
Verified at intake 2026-08-18: gate (net) + adversarial source check + contested-tag second coding.
Related briefs (distinct sub-problems, cross-referenced 2026-08-18): `circular-economy-battery-black-mass-classification-divergence`, `energy-lfp-battery-recycling-economics`.
Reconciliation 2026-09-29: The whole write-up was read against both cited sources. The paper (Bilfinger et al. 2025) was fetched in full on 2026-09-29 from https://www.nature.com/articles/s44406-025-00010-8, and its citation record from https://api.crossref.org/works/10.1038/s44406-025-00010-8. The European Commission page was fetched in full on the same day from https://single-market-economy.ec.europa.eu/single-market/digital-product-passport/batteries_en. The page's own record says it was last modified on 2026-08-21, which is after the date this write-up first read it, so the page may have changed in between. (1) The text said "the Commission's July 2026 implementing decision adopted six of the eight CEN-CENELEC JTC 24 harmonised standards for the passport's data architecture." The Commission page lists "July 2026: Implementing decision on the adoption of six of the eight harmonised standards developed by CEN-CENLEC JTC24" under a timeline that it calls indicative. It does not say the decision has been taken, and it does not say what the standards cover. The sentence now reports the timeline entry as the page gives it. The earlier paragraph in these notes still describes the decision as adopting the standards and should be read with this correction. (2) The text called the Battery Pass consortium "the publicly funded German initiative." The paper calls it "a publicly funded initiative uniting strategic partners in the field of EVs" and does not give a country. The word "German" was taken out. (3) The text ended one section by saying that the emissions world moved from manufacturer-declared figures to standardised in-use tests after the diesel scandal. Neither source mentions this, so the sentence was taken out. Confirmed against the paper and left as written: the Source line (seven authors, title, npj Clean Energy volume 1, article 10, published 10 October 2025, Institute of Automotive Technology at the Technical University of Munich); the correction dated 31 December 2025, which changes only the title; every quotation in the write-up, each found word for word; UN Global Technical Regulation No. 22, its incorporation into Euro 7 and its use of the WLTC driving cycle; ISO 12405-4; the maximum charging power of 8 kW for a 120 kWh pack, below the 11 kW of a typical EU wallbox; the 30-minute rest; room temperature; ISO 15118 and IEC 61851; differential voltage analysis; and pack voltage having to be reverse-engineered from CAN data. Confirmed against the Commission page and left as written: 18 February 2027 as the date the passport becomes mandatory; electric vehicle batteries, batteries for e-bikes, e-mopeds and e-scooters, and industrial batteries as covered categories; and the two content headings quoted. NOT checked: the 2 kWh threshold for industrial batteries, the references to Annex XIII, Annex VII and Article 14, and the term "light means of transport" rest on Regulation (EU) 2023/1542 itself. The EUR-Lex copy of the regulation returned an empty page to two automated attempts, so these are left as written. Genes untouched.