Shipping a battery energy storage system (BESS) overseas requires more than arranging freight. Exporters must coordinate dangerous goods classification, battery safety, container integrity and carrier acceptance. For international sea transport, the IMDG Code 2024 Edition, incorporating Amendment 42-24, became mandatory on 1 January 2026. International Maritime Organization
Which UN number applies to BESS shipments?
Containerized lithium batteries installed in a cargo transport unit solely to supply external power generally fall under UN 3536, Class 9. Separately shipped lithium-ion batteries or batteries accompanying equipment may require UN 3480 or UN 3481. Classification depends on configuration, not simply the description “BESS container.” IMO
What does UN 38.3 require?
Lithium cells and batteries must satisfy applicable UN Manual of Tests and Criteria, subsection 38.3, requirements. Manufacturers and subsequent distributors must make the prescribed test summary available. Match it to the supplied battery model and review assembled battery provisions; a cell report alone does not automatically establish compliance for every battery assembly. PHMSA
The summary identifies the manufacturer, laboratory, tested product, report reference and test results. A Safety Data Sheet (SDS) does not replace the required test summary. Keep test reports accessible for additional technical review.
The summary must be available, but does not automatically need to accompany every shipment. Nevertheless, obtain the carrier’s document checklist early to satisfy its acceptance requirements. PHMSA
How must the system be prepared?
Special Provision 389 requires secure battery attachment, short-circuit prevention and protection against accidental operation or significant movement. Systems must prevent overcharge and overdischarge. Necessary firefighting or air-conditioning dangerous goods may remain properly secured; unrelated dangerous goods must not be added. IMO
Document a manufacturer-approved transport configuration before dispatch. Confirm electrical isolation, protective system status and state of charge with the carrier. Do not assume that air transport’s familiar 30% charge limit is a universal IMDG requirement for UN 3536. IMO
What maritime and structural rules apply?
UN 3536 has stowage Category D: on deck only on cargo ships, protected from heat sources and clear of living quarters. Apply the required Class 9 placards and UN number markings. IMO
Where the enclosure falls within the International Convention for Safe Containers, verify CSC approval and examination status. Confirm rated gross mass, lifting arrangements and securing design. For packed containers covered by SOLAS, provide verified gross mass before loading. Electrical safety certification cannot replace these checks. International Maritime Organization
For heavy systems, obtain written confirmation that terminal equipment, lifting arrangements and inland transportation can accommodate the actual unit weight and dimensions.
Which documents and approvals are needed?
Prepare an accurate dangerous goods transport document and the container/vehicle packing certificate where applicable. Coordinate the declaration with commercial shipping documents, battery identification and the physical shipment. The shipper’s declaration and packing certification have distinct responsibilities, even when combined on one form. GOV.UK
Obtain carrier dangerous goods approval before dispatch. Confirm destination and transshipment port acceptance, documentation deadlines and terminal dwell restrictions. Booking details must match the final declaration; changes can require renewed approval. Maintain accessible emergency contacts and share handling instructions with logistics partners. Maersk
Port policies also matter. Hapag-Lloyd’s London Gateway notice introduces additional charges from April 2026 when UN 3536 units remain uncollected beyond 24 hours after discharge. Such restrictions require coordinated customs clearance and collection planning. Hapag-Lloyd
Does shipping compliance authorize overseas installation?
No. Transport compliance and destination approval serve different purposes. UL 9540 addresses energy storage system safety, while UL 9540A evaluates thermal runaway fire propagation. Neither replaces dangerous goods transport requirements. Assess local installation, electrical and fire safety obligations separately. UL Solutions
Build transportation compliance into product design and procurement, rather than treating it as a final logistics task. Assign clear ownership for classification, documentation and release approval before the first shipment.
