IMDG vs. IATA: Key Differences for Battery Shippers

1. One Parent, Two Regimes: Why Harmonisation Is Only Partial

Freight forwarders who move lithium batteries by both sea and air routinely discover that a consignment which is entirely compliant in one mode is unacceptable in the other. That is not an administrative accident. It is the predictable result of a system in which a single technical source document is adapted independently by two very different transport industries, each with its own risk profile, its own governing treaty and its own revision cycle.

The common ancestor is the UN Recommendations on the Transport of Dangerous Goods, Model Regulations, maintained by the UN Sub-Committee of Experts and republished on a two-year cycle. The Model Regulations are not law anywhere. They are a template: they establish the classification criteria, the UN numbers, the packing group logic, the test series in the Manual of Tests and Criteria (Section 38.3 for lithium cells), the marking and labelling conventions, and the numbering of packing instructions. Every modal regime then takes that template and modifies it to fit the physics and the emergency response reality of its own mode.

The reason air diverges most is simple: an aircraft in flight cannot be stopped, cannot be boarded by an external response team, and offers no realistic means of isolating or jettisoning a cargo unit that begins to vent. A ship's crew can access a hold, flood a compartment, apply boundary cooling, or in extremis divert to a port of refuge. Aviation therefore treats uncertainty about a battery's internal condition as unacceptable, where maritime carriage treats it as manageable with sufficiently robust packaging.

2. Scope and Legal Basis: SOLAS and IMO vs. ICAO and IATA

The two regimes are not equivalent instruments, and understanding what each one actually is resolves a great deal of confusion about which document governs in a dispute.

The IMDG Code is published by the International Maritime Organization and is given mandatory force through Chapter VII of the SOLAS Convention and through MARPOL Annex III for marine pollutants. It is revised on a two-year cycle and issued as a numbered amendment. Amendment 42-24 became mandatory on 1 January 2026, following the customary voluntary application window during the preceding year. Because SOLAS is a treaty, the IMDG Code binds flag states, and through them shippers, packers and terminals.

Air is a two-layer structure, and this is where shippers most often go wrong. The legally binding instrument is the ICAO Technical Instructions for the Safe Transport of Dangerous Goods by Air, adopted under Annex 18 to the Chicago Convention. The IATA Dangerous Goods Regulations is not itself law: it is the airline industry's field manual, which reproduces the ICAO Technical Instructions and adds further restrictions agreed by IATA member carriers, plus state variations and operator variations. Where the DGR is stricter than the Technical Instructions, the stricter DGR provision is what an airline will enforce at acceptance, because the airline's own conditions of carriage apply. In practice, the DGR is the operative document for anyone tendering cargo to a commercial airline.

3. Classification and UN Numbers: Where the Two Agree

The good news for shippers is that the foundation is genuinely harmonised. Both regimes inherit classification wholesale from the UN Model Regulations, so a battery that is correctly classified for sea is correctly classified for air. Disagreement between the modes almost never concerns what the article is; it concerns what you are allowed to do with it.

Lithium cells and batteries are assigned to Class 9, miscellaneous dangerous substances and articles, across four UN numbers, differentiated by chemistry and by whether the battery travels alone, packed alongside equipment, or installed inside it.

Both regimes also share the same qualifying test requirement. Cells and batteries must have passed the applicable tests of sub-section 38.3 of the UN Manual of Tests and Criteria, and both require that a test summary be made available. Both apply the same threshold logic based on watt-hour rating for lithium ion cells and batteries and on lithium content in grams for lithium metal, and both use that logic to separate smaller consignments eligible for relief from full-regulation consignments.

Both regimes also carry the parallel special provisions that govern non-standard battery conditions: the provision covering damaged or defective cells and batteries, the provision covering cells and batteries shipped for disposal or recycling, and the provision covering prototypes and low-volume production runs. The texts are closely aligned. What differs, decisively, is whether the mode permits the resulting consignment to travel at all.

4. Packing Instructions Compared: P and LP Series vs. PI 965 to 970

This is the first area where the two documents look structurally unlike each other, and it is the most common source of preparation errors. The IMDG Code organises packing instructions by battery condition and packaging format. The IATA DGR organises them by UN number and configuration, then subdivides each instruction into sections by size and aircraft type.

The IMDG scheme uses the P series for standard packagings and the LP series for large packagings, with the two running in parallel: each condition category has a P instruction and an LP equivalent for a single large battery or a large item requiring a large packaging.

The IATA side maps onto UN numbers rather than conditions. Six packing instructions cover the whole of standard lithium battery carriage by air:

Within each IATA packing instruction, Section IA covers larger cells and batteries as fully regulated dangerous goods, Section IB covers smaller cells and batteries above the exception thresholds but below the Section IA size limits, and, where it still exists, Section II covers the smallest consignments with reduced requirements. For UN 3480 shipped alone, the Section II option has been withdrawn, so every standalone lithium ion battery consignment by air is a fully declared dangerous goods shipment.

The IMDG Code has no comparable sectioning. Relief for small cells and batteries is handled through the relevant special provision, and beyond that threshold the consignment is simply subject to P903 or LP903 with the associated marking, labelling and documentation. There is no maritime analogue to the IATA net quantity per package tables or to the cargo aircraft only distinction.

5. The Decisive Divergence: Damaged, Defective and End-of-Life Batteries

Everything above is detail. This section is the reason the two regimes cannot be treated as interchangeable, and it is the single fact that most often forces a routing decision in reverse logistics, warranty returns, recall handling and battery recycling.

The IMDG Code takes a fundamentally different position. Under the special provision governing damaged and defective batteries, Special Provision 376, a damaged or defective cell or battery may be carried by sea, provided it is assigned to the correct tier and packaged accordingly. The provision creates two tiers:

• Damaged or defective, but not liable to rapid disassembly. Batteries assessed as stable enough that a dangerous reaction, dangerous heat evolution or rapid disassembly is not expected. These are carried under P908, or LP904 where a single large battery requires a large packaging. The packaging must provide short circuit protection, cushioning, containment of any electrolyte release and a means of managing the consequences of a failure.
• Liable to rapid disassembly, dangerous reaction, flame or dangerous heat evolution. This is the high-hazard tier, and it demands the highest containment class: P911, or LP906 for large packagings. Certification at this level is not a drop and stack exercise. It requires demonstrated performance under an actual thermal runaway event, with limits on external surface temperature, on flame or projectile release, and on the escape of hazardous substances from the packaging.

The assessment that places a battery in one tier or the other must be made by a competent person against criteria set out in the regulation, and where the internal condition of a pack is genuinely unknown (accident-involved vehicles, water-damaged stock, unidentified recycling feed, packs with no retrievable battery management system data), the conservative and defensible assignment is the higher tier. Unknown condition is not the same as benign condition.

For an operation that handles end-of-life packs, this asymmetry is structural rather than incidental. Forward logistics of new batteries can use air freight when speed matters. Reverse logistics of damaged, recalled or end-of-life packs cannot use air at all, which means the network design for returns is a road and sea network by regulatory necessity, not by cost preference. Planning a returns flow around air freight and discovering the prohibition at the point of tender is an expensive and entirely avoidable failure.

6. State of Charge, Quantity Limits and Mode Restrictions

Where both modes permit a consignment, the operating envelopes still differ substantially. Air applies a state of charge cap, an aircraft type restriction and per-package net quantity limits. Sea applies stowage and segregation controls instead, and imposes no general state of charge cap.

The 30% state of charge cap deserves particular attention because it is frequently misremembered as a universal rule. It is an air requirement attached to standalone lithium ion batteries, and it exists because a partially charged cell in runaway releases less energy, vents less violently and propagates more slowly than a fully charged one. It reduces severity; it does not prevent the event. Applying a 30% state of charge discipline to sea consignments is sound practice and many shippers do it voluntarily, but it is not something the IMDG Code obliges you to do, and it does not substitute for correct packaging selection.

Sea carriage brings its own exposures that air does not. A container stowed on deck on a long ocean leg can spend weeks in direct sun, with internal temperatures well above ambient, followed by cold night cycling and salt-laden humidity. Under deck stowage removes the solar load but places the consignment in a confined space where a venting pack releases hydrogen, carbon monoxide and hydrogen fluoride into a volume that crew may later need to enter. This is precisely why the maritime regime is willing to carry damaged cells only in packaging that has been proven against a real thermal event.

7. Marking, Labelling, Documentation and Training Compared

Marking and labelling are broadly harmonised; documentation and training are not. The differences are procedural rather than conceptual, but they are exactly the differences that cause a consignment to be refused at acceptance.

Two documentation points cause disproportionate trouble. First, the Shipper's Declaration for air is unforgiving of formatting: the sequence of entries, the wording of the proper shipping name, the packing instruction number and the aircraft type must all be exactly as prescribed, and an acceptance check will reject a declaration for errors that a maritime document would tolerate. Second, the container packing certificate for sea places a signed personal responsibility on whoever packed the cargo transport unit, covering segregation inside the unit, securing of the load and the absence of damaged packages. Forwarders who treat it as a formality are signing an attestation they have not verified.

8. Practical Guidance for Multimodal Lithium Shipments

Most real lithium consignments are multimodal. A pack leaves a plant by road, crosses an ocean in a container, and completes the last leg by road or rail. Returns and recycling flows are almost always road plus sea. The planning rule that follows from everything above is straightforward to state and frequently ignored in practice.

A workable sequence for a forwarder handling a mixed lithium portfolio:

1. Establish condition before you establish routing. Damaged, defective, recalled or recycling-bound status removes air from the option set immediately. Document the assessment, by whom it was made and against which criteria, because you will be asked.
2. Classify to the UN number and configuration. This is common to both regimes, so it only needs doing once. Retain the UN 38.3 test summary and be able to produce it.
3. Select the governing regime for each leg. Air: the IATA packing instruction and section. Sea: the IMDG packing instruction. Road: the ADR packing instruction, which for lithium batteries maps closely onto the IMDG one.
4. Choose packaging that satisfies the strictest leg. For sound batteries this is usually straightforward. For damaged or unknown-condition packs it means certified containment at the P911 or LP906 tier, and it means accepting that the routing is road and sea.
5. Prepare the documentation set per mode. A Shipper's Declaration for air legs; a dangerous goods transport document plus container packing certificate for sea legs. Do not attempt to make one document serve both.
6. Verify the edition in force on the shipping date. Air changes on 1 January every year. Sea changes on a two-year amendment cycle, with Amendment 42-24 mandatory from 1 January 2026.

8.1 Where Certified Containment Simplifies the Problem

For sound, tested batteries in ordinary commercial flows, packaging selection is a routine exercise. The difficulty concentrates entirely in the damaged, defective, recalled and end-of-life population, where the assessment is uncertain, the consequence of getting it wrong is a thermal runaway event inside a container, and the highest regulatory tier applies.

Certified containment simplifies this in a specific and limited way: it collapses the decision. Rather than tiering each pack between P908 and P911, and each large battery between LP904 and LP906, a large packaging certified to UN LP906 already satisfies the highest tier, so the conservative assignment carries no additional packaging decision. It also removes a category of routing risk, because a single unit covers road, sea and rail legs without repacking at modal interfaces.

What certified containment does not do is create an air option. No packaging, at any certification level, makes a damaged, defective or end-of-life lithium battery acceptable as air cargo under the IATA DGR. For that population, sea and road are the available modes, and the correct planning assumption is that they always will be.

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