Battery Cell Serialisation: Why Marking at Cell Level Is Now Standard Practice
That approach will not satisfy the EU Battery Regulation. From 18 February 2027, EV batteries and industrial batteries above 2 kWh placed on the EU market must each carry a Battery Passport, a live digital record linked to a unique physical identifier on the battery. Annex XIII of the regulation is clear that this identifier must allow individual battery tracking, not just batch-level tracking.
In practice, this is driving the industry towards cell-level serialisation. Not universally, and not without debate about exactly where in the production sequence the mark belongs. But the direction of travel is clear. If your Battery Passport system requires a unique identifier for each unit, and your cell production runs at hundreds of thousands of units per day, you need to think carefully about how, where, and at what speed you apply that mark.
This article sets out why the shift to cell-level marking is happening, where in the production sequence the mark needs to be applied, and what a production-grade inline marking system looks like in practice.
From Pack-Level to Cell-Level: Why the Shift Is Happening
Battery traceability has been evolving for years, driven by automotive quality systems rather than regulation. Tier 1 automotive suppliers have long required module-level and increasingly cell-level data to support their production quality tracking, knowing which cells went into which module, which modules went into which pack, and which pack went into which vehicle.
The EU Battery Regulation formalises and accelerates this trend. Annex XIII specifies the data that must be included in the Battery Passport. Among the mandatory fields are serial numbers and batch identifiers that allow individual battery identification, not just model-level identification. For a Battery Passport to function as a live, unit-specific record, the physical identifier on the battery must be unique to that unit.
GS1, the global standards body for product identification, has published guidance on applying its identification standards to EV and industrial batteries under the regulation. Their guidance confirms that a serialised identifier, unique to each individual battery unit, is required for the Battery Passport to function correctly, and that this identifier should be indelibly printed or engraved on the battery as a QR code.
Article 38(6) of Regulation (EU) 2023/1542 puts it directly: manufacturers shall ensure that batteries which they place on the market bear a model identification and batch or serial number, or product number or another element allowing their identification.
At pack level, this is straightforward. One identifier per pack, applied to the housing. The challenge emerges when you consider second-life applications and recycling. An EV battery pack that is disassembled for second-life energy storage or recycling loses its pack-level identifier the moment the housing is opened. The individual cells, which retain their electrochemical history and material composition, have no individual identity unless they were marked at cell level.
This is the practical driver behind cell-level serialisation. The Battery Passport data needs to follow the cell, not the pack it arrived in.
Where in the Production Sequence Does the Mark Go?
Cell manufacturing is a long and chemically sensitive process. Not every stage is appropriate for marking, and the wrong choice creates real production problems.
| Stage | Production process | Marking feasibility |
|---|---|---|
| Cell assembly | Winding/stacking, welding, filling | No mark yet — open cell, active chemistry exposure risk |
| Cell sealing | Crimp or laser seal, electrolyte fill | No mark yet — surface state varies |
| Formation cycling | Initial charge-discharge, SEI formation | Mark can follow here — surface is stable, cell is sealed |
| Grading & testing | Capacity sort, OCV, internal resistance | Optimal point — cell is fully characterised, identity confirmed before dispatch |
| OCV / degassing | Rest, pressure check, final OCV | Mark at this point or before — both practical |
| Module assembly | Cells grouped into modules | Window closing — module adds access constraints |
| Pack assembly | Modules into pack, BMS, cooling | Pack-lev |
The practical consensus among process engineers working on battery cell traceability is that the mark should be applied after formation and before module assembly. The cell has a stable, sealed surface. Its performance characteristics are known. Its identity, once marked, can be linked immediately to its measured capacity, internal resistance, and batch data in the manufacturing execution system.
For cylindrical cells (18650, 21700, 4680 format), the curved outer surface is the marking target. For prismatic and pouch cells, the flat face or housing edge is more typical. Each geometry creates different constraints on marking system design, mark positioning, and readability verification.
The Throughput Challenge at Gigafactory Scale
Here is where most discussions of cell-level marking underestimate the engineering problem. A gigafactory does not produce hundreds of cells per shift. It produces hundreds of thousands.
Tesla’s Giga Texas facility has reported production rates of over 126,000 4680 cells per day from a single line at ramp-up stage, and full-scale gigafactory operations are designed to run multiple lines simultaneously. At those volumes, the marking station is not a bottleneck you can afford. It needs to match line speed without adding cycle time.
For a production line running at 200 cells per minute, a realistic figure for mature cylindrical cell production, a marking system needs to complete the full mark-verify cycle in under 300 milliseconds per cell. That includes positioning or rotating the cell to present the marking surface, firing the laser, reading and verifying the code against the ISO/IEC 15415 grading standard, and linking the verified identifier to the MES record before the cell moves downstream.
A 300-millisecond cycle is achievable with a properly specified fibre laser system and inline machine vision, but it requires careful integration. The laser parameters, cell fixture design, conveyor speed, and vision system must all be engineered together. An off-the-shelf laser and a separately purchased camera will not give you a reliable, production-validated system.
The throughput specification is usually the first conversation that separates a marking machine discussion from a marking system discussion. If your line speed is defined, work backwards from it. Every element of the marking station, including mark size, laser power, galvo speed, and verification dwell time, follows from that number.
What an Inline Cell Marking System Looks Like
A production-grade inline marking system for battery cells is not a single machine. It is a station: an integrated combination of components that need to work together reliably under production conditions, 24 hours a day, seven days a week.
The laser source. Fibre laser is the standard choice for cell-level marking on metallic housings, aluminium for prismatic and many cylindrical cells, steel for some cylindrical formats. A pulsed fibre laser in the 20W to 50W range gives sufficient power for fast marking at production speeds without creating heat-affected zones that damage the underlying material. For cells with coated or polymer-laminated surfaces, laser parameter optimisation is critical; the wrong settings will bubble or ablate the coating rather than mark it.
The cell handling system. Cylindrical cells present their identifier on a curved surface. This means either rotating the cell under a fixed laser head, or using a galvo-head system capable of marking on a curved surface without rotating the cell. Both approaches are used in production. The rotation approach is simpler and gives excellent mark quality. The galvo approach is faster but requires more sophisticated beam control. For high-speed lines, the cell handling system is often the primary constraint on cycle time, not the laser itself.
The vision verification system. Every marked cell needs to be verified before it moves downstream. Verification is not optional in a regulated traceability application; an unreadable mark is worse than no mark, because it creates a false record. The vision system reads the Data Matrix code, grades it against ISO/IEC 15415, and confirms the identifier matches the record created in the MES. Cells that fail verification are flagged and diverted before they enter module assembly.
MES integration. The marking station is only as useful as its connection to the production data system. Every verified identifier needs to be pushed to the MES immediately, with a timestamp, the formation data for that cell, and the production parameters from the marking station itself. This creates the data link that the Battery Passport will ultimately draw on. If the MES integration is missing or unreliable, the physical mark is present but the digital record it is supposed to anchor is not.
Cell Format Considerations
The three main cell formats each present different marking challenges.
Cylindrical cells (18650, 21700, 4680) have a curved surface, compact marking area, and the highest throughput requirement. The 4680 format offers more surface area than 21700, which eases mark size constraints, but still requires rotation or advanced galvo control.
Prismatic cells have a flat face that provides a straightforward marking surface. Lower throughput than cylindrical lines typically, but larger cell dimensions mean more options for mark size and position. Aluminium housing is well-suited to fibre laser marking.
Pouch cells are the most challenging format. The flexible outer laminate is sensitive to laser heat, and the cell itself lacks the rigid housing that provides a stable marking target. Marking on the tab or a rigid component attached to the cell is more common than marking directly on the pouch.
How Pryor Can Help
We design and build laser marking systems at our Sheffield headquarters. For battery cell serialisation applications, we engineer complete inline stations, laser source, cell handling, vision verification, and MES integration, specified to your cell format, line speed, and data requirements.
We are not a component supplier. We do not sell you a laser and leave you to assemble a system around it. Our engineers work through the throughput specification, cell geometry, mark size requirements, and verification criteria with you before a system is proposed. If your line speed requires a specific cycle time, we design to that specification.
If you are working through your cell-level serialisation specification, speak to our team. We are happy to advise on system design, mark placement, verification setup, and MES integration without any obligation.
Call: +44 (0)114 276 6044
Email: info@pryormarking.com