The digital battery passport is not a static document. For LMT batteries, EV batteries and stationary battery energy storage systems (SBESS), the passport must reflect the battery's current state of health throughout its life, and that data comes from the battery management system (BMS).

Since 18 August 2024, Article 14 of the Battery Regulation (EU) 2023/1542 has obliged manufacturers to store a number of specific parameters in the BMS and give read-only access to this data. When the battery passport becomes mandatory from 18 February 2027, a subset of the same parameters must be available in the passport and updated continuously.

This article goes through what Article 14 and Annex VII require in concrete terms, how data flows from the BMS to the battery passport, and how manufacturers can handle the requirement for open access without compromising business-critical information.

What does Article 14 require in concrete terms?

Article 14 sets three overall requirements for manufacturers of LMT batteries, EV batteries and stationary battery energy storage systems:

  • The BMS must store the Annex VII parameters. The battery management system must contain up-to-date data on the parameters needed to determine the battery's state of health and expected lifetime, as specified in Annex VII.

  • Read-only access for legally purchased batteries. The natural or legal person who has legally acquired the battery, or a third party acting on their behalf, must at all times have read-only access to the BMS data. The access must be usable to assess residual value, prepare reuse, second-life applications or recycling.

  • Software reset function. The BMS must have a software reset function, so independent operators can reset the configuration when the battery is repurposed, for example when an EV battery is to be reused as stationary energy storage.

The requirements apply from 18 August 2024, but implementation in practice is only now being tested, because it is only with the battery passport in 2027 that data must be available via a standardised electronic format.

Annex VII: the parameters that must be stored

Annex VII sets the minimum list of parameters the BMS must store. The list is not exhaustive – manufacturers can record more parameters – but these must be present:

  • Remaining capacity
    The current capacity relative to the rated capacity, expressed as a percentage or in energy units.
  • Capacity fade
    The rate at which capacity is reduced over time and cycles.
  • Remaining power capability
    The battery's ability to deliver power at peak load compared with the original specification.
  • Efficiency loss (round-trip efficiency fade)
    The total loss in charge and discharge efficiency over time.
  • Internal resistance
    The current internal resistance, which is a critical indicator of both performance and thermal safety.
  • Operating temperatures
    A history of operating temperatures, including exposure to temperatures outside the specified operating range.
  • Number of charge and discharge cycles
    The number of full-cycle equivalents and a log of charge and discharge patterns.
  • Negative events
    Records of events with extreme temperatures, overcharging or deep discharge.

For batteries placed on the market after 18 August 2024, these parameters must be stored continuously and be available throughout the battery's life.

State of Certified Energy: a separate requirement for electric vehicles

For EV batteries, the regulation introduces a specific and often misunderstood concept: State of Certified Energy (SOCE). SOCE is not the same as State of Health (SoH).

SoH is an internal, manufacturer-specific metric that describes the battery's state of health relative to its original capacity. SOCE is a certified, standardised measurement method used for type approval and harmonised with the UNECE technical regulations (GTR 22).

The difference matters in practice. When an EV battery is assessed for residual value or second-life use, an SoH value from manufacturer A and manufacturer B cannot necessarily be compared directly, because the measurement methods can differ. SOCE solves that problem by defining a common test procedure, so the battery's remaining energy can be certified across manufacturers.

Both values must be available in the battery passport for EV batteries. SoH provides the ongoing operational insight, SOCE provides the certifiable value for market transactions and recertification.

How does data flow from the BMS to the battery passport?

The regulation does not specify a particular technical protocol between the BMS and the battery passport. It only prescribes that the data must be available in a standardised, machine-readable form, and that it must be accessible via the QR code on the battery.

In practice, this requires a data pipeline with three layers:

  • The BMS layer. The BMS records the Annex VII parameters in real time and stores them in internal memory. Communication with the outside world typically happens via CAN bus, ISO 15118 (for EV) or proprietary protocols for industrial batteries.

  • The aggregation and translation layer. Raw data from the BMS must be translated into the standardised data formats required by the battery passport. This is where the semantic mapping happens: a BMS value called "cell_capacity_remaining_pct" must be mapped to the data point standard used in the passport (typically following DIN DKE SPEC 99100 or the IDTA submodel for the battery passport).

  • The battery passport layer. The passport itself exposes the data via a REST API or an equivalent interface accessed via the QR code. The data must be correctly timestamped, so recipients can judge how fresh it is.

For LMT and EV batteries, the aggregation will typically take place in a cloud backend, where the BMS periodically uploads data via the vehicle's or the app's communication module. For stationary systems, it often happens directly from the installation's gateway.

Requirements for update frequency

The regulation does not require a specific update frequency, but the data must be "up to date". In practice, this is interpreted differently depending on the battery category:

  • For EV and LMT batteries, updates are expected at least daily or after each usage cycle.
  • For stationary systems, weekly updates are typically acceptable, as the operating pattern is more constant.
  • For safety-critical parameters (internal resistance, temperature events), alarms must be able to trigger in near real time.

The specific intervals are expected to be clarified in the implementing acts the Commission must adopt before February 2027.

Who has access to what?

One of the most overlooked aspects of Article 14 is access control. BMS data is not public: access is role-based and defined by both Article 14 and Annex XIII (which specifies the battery passport's access levels).

There are four types of data consumers:

  • The battery's owner or a third party acting on the owner's behalf. Has read-only access to all Annex VII parameters in the BMS, whether the data goes via the passport or directly from the BMS. This includes independent workshops and diagnostics companies.
  • Recyclers and repurposing operators. Get access to SoH data and event history to assess the battery's suitability for second life or material recovery. Access can be via the battery passport without a direct BMS connection.
  • Notified bodies, market surveillance authorities and the Commission. Have extended access rights defined in Annex XIII, including data on compliance and type approval.
  • End-users and the public. Only get access to the limited subset of data designated as public in Annex XIII, typically the overall state of health, not detailed diagnostic data.

For manufacturers, this means they must build a differentiated access model, where different roles see different subsets of the same underlying data.

The tension between openness and trade secrets

The requirement for read-only access to BMS data has created considerable friction in the battery industry, especially among large EV manufacturers who fear that opening access could expose algorithmic IP around battery management, or that competitors could reverse-engineer chemistry-specific operating patterns.

The regulation recognises the issue. Article 14 explicitly specifies that access is read-only, and that it only covers the Annex VII parameters, not the manufacturer's internal BMS algorithms, calibration constants or proprietary control logic.

That gives manufacturers a manageable boundary:

  • The Annex VII parameters are exposed. This is raw data on the battery's condition, not how the BMS calculates it.

  • Algorithms and calibration remain closed. How a manufacturer estimates SoH based on voltage and current curves remains IP.

  • Data can be abstracted through a data layer. The manufacturer does not have to give direct access to the BMS itself. Access can be provided through a secured API or the battery passport, where the standardised parameters are presented without exposing the underlying implementation.

The architectural consequence is that manufacturers must establish a well-defined data layer between the BMS and the battery passport that both meets the requirement for openness and protects the underlying IP. It is a design task that should be built into the BMS architecture from the start, not retrofitted close to 2027.

The link to the battery passport and second life

BMS data is one of the most valuable components of the digital battery passport. While the carbon footprint and recycled content are static declarations, health data is live, and it is what makes the passport useful to recyclers, repurposing companies and insurers.

An EV battery that has reached 70% SoH after 8 years in the car can still have considerable value as stationary energy storage for another 5-10 years. But only if the recipient can trust the data. This is where the battery passport becomes critical: it acts as the neutral layer where BMS data from the manufacturer is documented, certified and made available to third parties.

For manufacturers, this also means that the quality of the BMS data directly affects the battery's remaining commercial value. Poorly calibrated SoH estimates or missing history can reduce the secondary market price a battery can achieve.

Summary

Article 14 and Annex VII are the technical backbone of the battery passport for LMT, EV and stationary batteries. The requirements have been in force since August 2024, but it is only when the battery passport takes effect in February 2027 that the integration must be operational.

Manufacturers should already now:

  • Verify that the BMS stores all Annex VII parameters with sufficient granularity and history
  • Design a data pipeline that maps BMS values to the standardised formats in the battery passport data model
  • Establish a differentiated access model that separates public data, owner data, authority data and confidential internal BMS algorithms
  • For EV batteries: plan the implementation of both SoH and SOCE

The complexity does not lie in the individual parameters: it lies in connecting them. A battery passport is only as reliable as the BMS data it is built on, and only as useful as the access control that gives the right actors access to the right data at the right time.