A unique identifier is the string that uniquely identifies an individual battery and resolves, through the data carrier, to its battery passport. Under Regulation (EU) 2023/1542 the identifier must be consistent with the ISO/IEC 15459 family of standards for unique identification, encoded in a QR code conforming to ISO/IEC 18004. Because Article 77(1) requires one passport per physical battery, the unique identifier must distinguish each individual battery rather than a model, type, or production lot.
The identifier is the anchor of the whole passport system: it is what the QR code carries, what the resolver looks up, and what guarantees that the record returned corresponds to exactly one physical battery.