What does UN3536 describe?

The IMDG Code lists “LITHIUM BATTERIES INSTALLED IN CARGO TRANSPORT UNIT” as the proper shipping name, with lithium-ion or lithium-metal batteries identified in the entry. Its Dangerous Goods List entry assigns Class 9 and Special Provision 389. The Code describes the unit as a mobile power supply unit. The IMO states that the 2024 IMDG Code edition, incorporating Amendment 42-24, became mandatory on 1 January 2026. [Sources: IMO current edition and UN3536 entry].

“Cargo transport unit” is a transport term, not simply a sales description for a metal enclosure. The relevant questions are whether the lithium batteries are installed inside that unit and whether the unit is designed only to supply power outside itself. A system drawing, battery installation record and functional description are more useful for this purpose than a product brochure alone.

This article uses the sea-transport IMDG Code as its regulatory reference. Origin and destination road legs, national rules and any other transport mode must be checked separately. The sea classification alone does not show that every connecting leg is prepared correctly.

Is this BESS shipment within the UN3536 entry?

Use the table to decide which question to put to the shipper's dangerous-goods specialist. It does not assign an alternative UN number to an unverified design.

The distinction is supported by the IMDG Code's treatment of installed batteries and Special Provision 389. A lithium-ion pack shipped on its own, for example, cannot be converted into UN3536 merely by loading it into a freight container. For the separate battery/equipment distinction, see our UN3480 vs UN3481 guide; that guide does not replace a UN3536 review. [Source: IMO Special Provisions 388–389].

What must be checked under Special Provision 389?

Special Provision 389 is narrower than “a battery in a container.” For the applicable UN3536 unit, it calls for lithium batteries meeting the referenced IMDG battery provisions, systems to prevent overcharge and overdischarge between batteries, and secure attachment to the unit's interior structure. That attachment must protect against short circuits, accidental operation and significant movement during normal transport shocks, loads and vibration. The provision also distinguishes dangerous goods needed for safe and proper operation of the unit from goods that are not needed and therefore must not be transported inside it. [Source: IMO SP389 text].

A useful evidence request is therefore specific: identify the cell and battery models; provide the relevant test and design information; show how racks, cabinets or other supports secure the batteries; explain the battery-management and protective systems; and list any other dangerous goods installed inside the unit. An SDS can help identify a product, but it does not independently prove that this particular installed configuration meets SP389.

For sea carriage under SP389, the batteries inside the cargo transport unit are not subject to separate marking or labelling requirements under that provision. The cargo transport unit must display the UN number and be placarded on two opposing sides as specified by the IMDG Code's referenced sections. This is a sea-rule statement, not an instruction for every inland leg. The exact presentation should be checked against the current code and the shipper's dangerous-goods adviser for the unit that will actually be offered. Do not copy a label illustration from another shipment or treat a Class 9 placard as carrier approval. [Source: IMO SP389 marking and placarding provisions].

What information should be ready before asking for a booking?

A carrier or freight forwarder cannot assess an unidentified “20-foot BESS.” Prepare one consistent cargo record that describes the unit as shipped, not only as it will operate at the final site:

1. Configuration and function: system model, drawings, whether lithium batteries are installed, where they are mounted, and whether the unit is designed only to provide external power.
2. Battery evidence: chemistry, manufacturer and model, battery quantity and ratings, applicable test-summary information, condition, and protective-system description.
3. Transport-unit facts: exact external dimensions, verified gross mass, centre of gravity, lifting points, handling/stacking limitations and any non-standard footprint.
4. Safe handling: isolation and shutdown method, emergency contact information and any installed fire-protection or cooling components that affect the transport review.
5. Other contents: a list of equipment and any dangerous goods inside the unit, with their reason for being there.
6. Movement plan: collection point, export terminal, proposed vessel/route, discharge terminal, inland delivery point, responsible parties and desired readiness date.
7. Document ownership: who will make and sign the dangerous-goods declaration, who supplies test/design evidence, and who resolves carrier or terminal questions.

These are pre-booking inputs, not a universal list of documents legally required for every move. The responsible shipper and qualified dangerous-goods personnel should determine the declaration and documentation under the applicable rules; the operator may request additional technical information.

Why classification does not guarantee a sea booking

A correctly supported UN3536 classification does not answer every operational question. Vessel operators and terminals may need to review the actual unit design, mass, lifting arrangement, stowage and emergency information before accepting it. Collection and delivery may introduce separate road, lifting and site-access constraints. A route that works for a standard dry container should not be assumed suitable for an unusually heavy or non-standard BESS unit.

Confirm four handovers before promising a schedule:

This is an operational planning framework, not a claim that each named party has the same legal responsibility in every country. Record the accountable party for the actual contract and jurisdiction. If one gate is unresolved, the quotation or sailing plan should be described as conditional.

For the commercial service scope and a China-origin project conversation, see Shipping Energy Storage Container from China. That service page and this classification guide answer different questions.

A pre-booking stop/go checklist

Before requesting a firm booking, the team should be able to answer yes to all of the following:

• Is the installed-battery configuration and external-power function documented for the exact unit being shipped?
• Has a qualified person reviewed the proposed UN3536 entry and the applicable SP389 conditions, including battery evidence, electrical protection, secure mounting and permitted contents?
• Are the unit's measured mass, dimensions, centre of gravity and approved lifting/handling method available?
• Is the condition of the batteries and system known, with any damage, defect, recall or abnormality explicitly disclosed?
• Has the shipper identified the dangerous-goods document owner and supplied the operator's requested technical evidence?
• Have the vessel operator, origin and destination terminals, and each required inland leg been checked for the particular cargo and route?

If the answer is no or unknown, do not resolve the uncertainty by changing a label or copying an earlier declaration. Identify the missing fact, assign an owner and obtain the required classification or operational acceptance before treating the move as bookable.