- UN3536 covers lithium batteries installed in cargo transport units -- BESS containers, EV-laden trailers, battery-integrated equipment modules. Not for loose batteries in boxes.
- Under IMDG Amendment 42-24 (mandatory 2026), UN3536 stowage moved to Category D -- on deck only, prohibited under deck and on passenger ships entirely. This was a direct response to the 2023 Genius Star XI fire.
- China enforces domestic SoC guidance (20--50% depending on port) and requires series/parallel circuit disconnection per JT/T 1543-2025. The US has proposed a statutory 30% SoC limit.
UN3536 is not just another battery UN Number. It is the classification for large lithium battery systems that are built into the structure of a cargo transport unit -- think a 40-foot container full of battery racks for grid storage, or a trailer carrying an electric excavator with the battery integrated into its chassis. These are not batteries in boxes. They are batteries that are part of the vehicle or container itself.
This distinction matters because the risks are different. A pallet of loose Li-ion cells can be isolated and cooled if one goes into thermal runaway. A 800 kWh battery energy storage unit inside a sealed container is a different problem. When that catches fire, you cannot get to individual cells. The CO2 system does not stop thermal runaway. And if the container is below deck, the crew has no practical way to fight the fire at all.
The Incident That Changed Everything
In December 2023, the vessel Genius Star XI was crossing the North Pacific from Vietnam to California with 192 BESS units classified as UN3536. Each unit held up to 800 kWh. Heavy weather (19-22 foot seas) caused cargo to shift. Lashing hooks, incompatible with the D-rings they were attached to, failed. D-ring brackets tore from the deck. BESS units broke loose and sustained physical damage.
The result: fire in cargo hold no. 1 on December 25. The crew discharged the CO2 system. A second fire broke out in cargo hold no. 2 on December 28. With no CO2 remaining, the crew used seawater and fire hoses. The vessel diverted to Dutch Harbor, Alaska. Damage estimate: $3.8 million. The NTSB investigation found 43 of 160 BESS units damaged, 41 units broken loose from lashings, three fire origin points.
Two additional US incidents followed in 2024: a truck rollover with BESS fire in Baker, California (highway closed for two days) and another near the Port of Los Angeles (multiple marine terminals closed for 1.5 days). These three incidents, documented in UN/SCETDG/65/INF.33 (November 2024), drove the regulatory response.
What Changed as a Result
The regulatory response came quickly on multiple fronts:
IMDG Amendment 42-24 (mandatory 2026): UN3536 stowage category changed to D. On deck only. No under-deck stowage. Prohibited from passenger ships entirely. Cargo transport units must be protected from heat sources and kept clear of living quarters.
UN Sub-Committee (November 2024, 65th session): UN3536 is being split into three separate UN numbers, effective 2026 through the 24th revised edition of the Model Regulations: UN3536 for lithium-ion batteries in CTUs, UN3563 for lithium metal batteries in CTUs, and UN3564 for sodium-ion batteries in CTUs. The reason: the Emergency Response Guide (ERG 2024) specifies entirely different firefighting procedures for lithium-ion (Guide 147) versus lithium metal (Guide 138). First responders need to know which chemistry they are dealing with.
China domestic requirements: No uniform national SoC limit, but port-level enforcement has emerged. Shanghai MSA recommends 20--50% SoC. Shandong MSA recommends below 50%. Lianyungang MSA's 2025 Operations Guide enforces JT/T 1543-2025 (effective May 2025), which requires battery series and parallel circuits to be physically disconnected during transport.
US proposed legislation: The Thermal Runaway Reduction Act (H.R. 9588, September 2024) would mandate batteries at no more than 30% SoC for transport.
The Compliance Trap: SoC Fragmentation
Here is where UN3536 gets operationally dangerous. The IMDG Code imposes no mandatory international SoC limit. But that does not mean SoC is unregulated. It means every jurisdiction is setting its own rules, and they differ.
You load a BESS unit at 50% SoC because that is acceptable at the Chinese port of loading. The vessel arrives in the US. The receiving terminal wants 30% or below because that is what proposed US legislation requires. Or the flag state has its own circular. Or the P&I club has its own conditions. You are compliant at origin and non-compliant at destination -- with no way to discharge a sealed 800 kWh unit sitting on the dock.
The practical move: check SoC requirements for the port of loading, the flag state, the port of discharge, and any transit ports. Document the SoC. Have a test report. And assume the most restrictive limit applies if your route crosses multiple jurisdictions.
The Documentation Required
A UN3536 shipment requires a full documentation package. You need: Dangerous Goods Declaration identifying UN3536 and the battery specifications, a Safety Data Sheet covering the battery system, a UN38.3 Test Summary confirming the batteries passed the UN Manual of Tests and Criteria, a Container Inspection Certificate confirming CSC compliance, and a Container Packing Certificate. The container must bear Class 9 placards and the UN3536 identification number on two opposing sides.
Frequently Asked Questions
What is the difference between UN3536 and UN3480/UN3481?
UN3480 is standalone lithium-ion batteries (batteries in boxes, not installed in anything). UN3481 is batteries packed with or contained in equipment (your laptop in its shipping carton). UN3536 is large lithium battery systems installed in cargo transport units -- BESS containers, battery-integrated vehicles, power modules that are structurally part of the transport unit. The scale is different. The firefighting challenge is different. The regulatory provisions reflect both.
What are the key compliance requirements for UN3536 shipments?
Class 9 placards and UN3536 marking on two opposing sides of the CTU. CSC-compliant container. Dangerous Goods Declaration. SDS covering the battery system. UN38.3 Test Summary. Container Inspection Certificate. Container Packing Certificate. Under IMDG Amendment 42-24: on-deck stowage only (Category D), clear of living quarters, protected from heat sources. Under Chinese requirements: SoC per port guidance, and circuit disconnection per JT/T 1543-2025. Check all jurisdictions on your route for SoC limits.
Related Terms
- IMDG Code -- The maritime regulatory framework governing UN3536 shipments, including the Amendment 42-24 stowage category D change.
- IATA DGR -- Air mode provisions for lithium battery shipments, including UN3536 with SoC limits strictly enforced.
- DG Packaging Certificate -- While UN3536's installed-battery provisions are less packaging-intensive, all DG documentation must be properly certified.