Model vs unit layer record: keeping shared data and single battery data apart

Every battery passport contains two kinds of information. Model information describes the battery model and is shared by every unit of that model. Unit information describes one individual battery and changes as that battery is used. Article 77(2) and Annex XIII organise the passport around that distinction, with points 1 to 3 addressing model information and point 4 addressing individual battery information. Confusing the two layers is the most persistent reading error in passport work.

A model figure read as a unit measurement overstates what is known about the battery in front of the reader. A unit event read as a model property misleads every other unit of the same model.

What belongs in the model layer?

The model layer holds manufacturer identity, model identifier, category, chemistry description, rated capacity and voltage, weight, place of manufacture where required, and the declaration of conformity reference. It also holds carbon footprint information, recycled content information, performance and durability parameters, and waste prevention information at model level, together with detailed composition, dismantling information and safety measures in the authorised and authority tiers. Model fields are stable. A change to a model field normally means a new model version, a new declaration reference, or a corrected record with a version note. Model fields are verified against technical documentation and test reports, not against the history of one battery. A reader who sees the same model values on two different unit records is seeing correct behaviour, not duplication.

What belongs in the unit layer?

The unit layer holds the unique identifier, the serial or unit number, the manufacturing date or batch reference, and everything that results from the use of that battery. Annex XIII point 4 lists unit level performance and durability values, state of health information, status changes and use phase events. The unit layer is the only layer that grows over time in normal use. Entries are dated, sourced and ordered. A unit layer that never changes after placing on the market may be accurate for a battery that has not been used, measured or serviced, but a unit layer that never changes for a battery in active service raises a question about whether history is being captured. The unit layer answers a different question from the model layer: not what was this battery designed to be, but what has happened to this battery.

How can a misplaced field be recognised?

A misplaced field shows one of three signs. The first sign is a value that is identical across every unit record but is presented as a measurement of the single battery, such as a carbon figure shown as if measured on that unit. The second sign is a value that differs between units of one model but is presented as a model property, such as a state of health figure copied into the model summary. The third sign is a field with no date and no source in a layer where dates and sources are the point, such as an undated status change in the unit history. Each sign calls for the same remedy: move the field to the correct layer, add the missing date or source, and record the correction as a version change rather than a silent overwrite. The table below summarises the test.

Why does the distinction affect access tiers?

Access tiers in Annex XIII cut across the two layers. Public model information sits in point 1. Model information for persons with a legitimate interest sits in point 2. Authority only model information sits in point 3. Individual battery information sits in point 4, for persons with a legitimate interest. A reader in the public tier therefore sees model information only, and must not infer unit history from its absence. A reader in the authorised tier sees model detail plus unit history, and must keep the two apart when quoting figures. The tier structure protects detailed composition and test reports, and it also protects the meaning of figures: a figure quoted without its layer and tier is an incomplete quotation. Record systems that flatten layers into a single view invite exactly that error, because the flattening removes the context that gives a figure meaning.

How should version changes be recorded across layers?

A model revision creates a new version of the model layer, with a version identifier and a date, and unit records created after the revision point to the new version. Unit records created before the revision keep their link to the version in force when the battery was placed on the market, unless a correction requires repointing. A correction to a model field is recorded as a correction, with the previous value retained in the version history where the system provides for it. A unit correction is recorded as a new dated entry that supersedes the earlier entry, not by deleting the earlier entry. Deletion destroys the audit trail that a later reader needs to understand why a value changed. Version discipline is a record discipline, not a display preference: the display can show the current value, but the record must retain the sequence.

What does a correct reading sound like?

A correct reading names the layer before the figure. It states that the capacity is a model rating, that the state of health is a unit measurement dated on a stated day, that the carbon figure is a model declaration for a stated manufacturing plant, and that the dismantling detail is model information in the authorised tier. That form of reading is slower than quoting a number alone, and slower is the point. The passport is a record, not a label, and records earn trust by showing scope, date and source alongside every figure. This guide gives general educational information only and does not give legal advice for a particular battery or record system.