Lithium batteries ship as Class 9 dangerous goods. You need the right UN number (3480/3481/3536), a UN 38.3 test summary, an SDS, a Dangerous Goods Declaration, UN-spec packaging and about 30% state of charge. Sea is the only practical mode for BESS-scale volumes, and mis-declaring gets the container refused or seized.
If you are an EPC contractor, energy developer, distributor or C&I business importing a containerised storage system from 100 kWh or project-scale LiFePO4 batches, your cargo is Class 9 dangerous goods, and the shipping line is fully entitled to refuse it. The short answer: lithium batteries move under the IMDG Code as UN 3480 / UN 3481 / UN 3536, backed by a UN 38.3 test summary, a Safety Data Sheet (SDS), a Dangerous Goods Declaration (DGD), UN-certified packaging with correct marking, and a state of charge of 30% or less. Get this set wrong and one of two things happens: the container is refused at port, delayed and fined — or, if the batteries were hidden under another commodity, the shipment moves illegally and with no valid insurance. Below is the working checklist to move BESS the right way.
Why lithium batteries are Class 9 dangerous goods
A lithium-ion cell packs a lot of energy into a small volume. If it is damaged, short-circuited, overheated or carries a manufacturing defect, it can enter thermal runaway — a self-sustaining reaction that vents flammable and toxic gases, ignites, and can re-ignite even after it appears to have been extinguished. That is why the UN lists lithium batteries under Class 9 (miscellaneous dangerous substances and articles), and why sea transport is governed by the IMDG Code — the International Maritime Dangerous Goods Code maintained by the IMO.
Key for 2026: IMDG Code Amendment 42-24 is in force and mandatory from 1 January 2026 (verify the current amendment at the time of shipment). Among other changes, it tightened how containerised BESS may be stowed on a vessel. This is not red tape for its own sake — it is precisely why lines scrutinise these bookings far more than ordinary cargo.
The three UN numbers and when each applies
The most common mistake buyers make — and the point competing articles gloss over — is confusing the three UN numbers. A containerised BESS does not ship under UN 3480. Choose correctly:
- UN 3480 — lithium-ion batteries shipped on their own (cells, modules or packs alone, with no equipment). For example, a batch of LiFePO4 cells sent for assembly.
- UN 3481 — lithium-ion batteries contained in equipment or packed with equipment (the battery powers the device it is built into or ships with).
- UN 3536 — lithium batteries installed in a cargo transport unit — i.e. a containerised storage system where the container itself is the product enclosure, integrating battery modules, the BMS, thermal management and fire suppression. This is the number most industrial BESS ships under.
UN 3536 carries Special Provision 389: the modules must be firmly secured inside the container to prevent movement, short circuits and vibration damage in transit. Under IMDG 42-24, containerised BESS is assigned Stowage Category D — on-deck only, with codes SW1 (protected from heat) and SW2 (away from living quarters). That directly limits how much vessel space is available to you.
The mandatory document and packaging set
This is the heart of a legal shipment. Miss a single document and the booking is rejected or the cargo is held at the terminal. The minimum set:
- UN 38.3 Test Summary — the report proving the battery passed eight test procedures (T.1–T.8: altitude, thermal cycling, vibration, shock, external short circuit and more) under Section 38.3 of the UN Manual of Tests and Criteria. Required for batteries above 100 Wh; lines often demand a summary no older than 12 months. How to read and validate it is covered in our guide to BESS certification: UN 38.3, IEC and system safety.
- SDS / MSDS — a safety data sheet in IMDG structure; Section 14 (transport information: UN number, class, packing group) is critical.
- DGD (Dangerous Goods Declaration) — the declaration by which the shipper formally states Class 9 and the UN number to the line.
- Container/Vehicle Packing Certificate — certifying correct loading and securing inside the container.
- UN-certified packaging per the applicable IMDG packing instruction, bearing the lithium battery mark, Class 9 labels and the UN number.
- State of charge of 30% or less (SOC ≤ 30%) — for containerised BESS this is now a requirement, not a suggestion; for batteries shipped alone (UN 3480), major lines such as Maersk and COSCO also enforce 30% in practice and may ask for SOC evidence before acceptance.
- Booking on a DG-approved vessel — dangerous-goods space is booked well ahead, realistically a month or more rather than the usual 2–3 weeks. Each booking is assessed as an individual risk, even for factories on a line's "white list".
The UN number on all these documents must match the actual cargo — otherwise it is a mis-declaration.
A BESS container is not stopped by the battery but by the wrong paperwork: a mismatched UN number, an expired UN 38.3 or a missing DGD, and your project sits in port.
Sea versus air, and why air is impractical for BESS
For containerised BESS and large battery batches there is really only one realistic mode — sea. Air freight of lithium batteries is heavily restricted: UN 3480 (batteries alone) is effectively banned on passenger aircraft, cargo flights carry strict Wh and quantity limits per package, and 30% SOC has long been mandatory by air. Multiply that by the weight and dimensions of a container system and air becomes both economically and physically impractical. So the whole chain is planned around ocean FCL and the IMDG Code.
The mis-declaration trap — and why full-cycle handling matters
The temptation is obvious: declare the batteries as "electrical equipment" or "spare parts" to save on the DG surcharge and squeeze into scarce space. It is the worst possible choice. Hidden batteries are, first, a breach of law (mis-declaration with real fines and carrier blacklisting), second, a direct safety hazard to the vessel and crew, and third, grounds for voiding your insurance: if there is an incident with undeclared cargo, the insurer walks away and the loss falls on shipper and consignee.
That is why cheap "just freight" from a random forwarder is a hidden liability. What you need is full-cycle handling: verifying cell grade at the factory, confirming certificates are present and valid, packing correctly to IMDG, preparing the DGD and booking DG space. This is where certification, your Incoterms 2020 terms (who is responsible for DG paperwork and where risk transfers) and pre-shipment quality inspection all converge.
How Silk Way Sourcing handles dangerous goods end-to-end
We work full-cycle: factory search and verification → cell and certificate checks → production and QC → logistics. For DG that means confirming the batch has a valid UN 38.3 summary and a current SDS, and that the factory declares the correct UN number (3480/3481/3536 for your case); arranging UN packaging, marking, the DGD and packing certificate; agreeing SOC ≤ 30%; and booking DG-approved vessel space ahead of time. Across 7 years (founded 2019) and 3,500+ delivered orders we move cargo so the container does not stall in port and the project starts on schedule. For the wider chain, see our guide to importing BESS from China and our BESS and storage sourcing service.
Planning a containerised BESS or a LiFePO4 batch? Email contact@silkwaysourcing.com or WhatsApp +380 97 883 4765 and we will organise compliant battery shipping with the full DG document set. Subject line: "Organise compliant BESS shipping with DG paperwork".
