Unimasters | 19/05/2026
IMDG 42-24 and ADR 2025: What Changed for BESS Transport on 1 January 2026
Series
IMDG/ADR Decoded: The Regulatory Handbook for BESS Transport
IMDG Code Amendment 42-24 became mandatory on 1 January 2026, replacing Amendment 41-22 after a 12-month transitional period. The amendment was adopted by IMO Resolution MSC.556(108) in May 2024. For road transport, ADR 2025 entered into force on the same date, harmonized with the UN Model Regulations 23rd Edition.
The authoritative texts are:
In plain terms: these amendments restructured how lithium batteries-including those in Battery Energy Storage Systems (BESS)-are classified, stowed, and documented. The changes reflect lessons learned from maritime incidents and the explosive growth of battery shipments since 2020.
BESS containers shipped from Asia to CEE construction sites fall under UN3536: LITHIUM BATTERIES INSTALLED IN CARGO TRANSPORT UNIT. This classification applies when lithium-ion or lithium-metal batteries are installed in a cargo transport unit (the container itself) and designed to provide power external to that unit-which describes every utility-scale BESS container on the market.
The 2026 amendments changed three critical parameters for UN3536:
For procurement teams planning BESS shipments, this means:
The distinction between UN3536 and other lithium battery classifications matters enormously. The Power Conversion System (PCS) in a BESS installation is NOT dangerous goods-it is a transformer station with no hazard class. Only the battery containers require DG classification.
This is the headline change for BESS logistics. Under Amendment 41-22, UN3536 was Stowage Category A, permitting both on-deck and under-deck stowage. Amendment 42-24 reclassified UN3536 to Stowage Category D.
Per IMDG Code Section 7.1.3, Stowage Category D means:
The practical impact: carriers now allocate UN3536 cargo to on-deck positions only. On-deck space is finite and weather-exposed.
Amendment 42-24 added two stowage codes to UN3536:
These codes formalize what responsible carriers already practiced, but they now create enforceable requirements.
While not directly applicable to stationary BESS, the new vehicle classifications affect EPC companies shipping mobile battery units or construction equipment:
The previous generic classification UN3171 (Battery-powered vehicle) is no longer permitted for lithium or sodium-ion powered vehicles. Shipments declared under UN3171 for lithium-powered equipment will be rejected.
Amendment 42-24 introduced a new Section 2.9.5 for sodium-ion batteries:
While sodium-ion BESS remains rare in utility-scale applications, some manufacturers are piloting sodium-ion systems for grid storage. The regulatory framework now exists for their transport.
The ≤30% State of Charge (SoC) requirement for standalone lithium-ion batteries (UN3480) shipped by sea remains unchanged. For UN3536 BESS containers, Special Provision 389 applies, which requires batteries to "contain the necessary systems to prevent overcharge and over discharge between the batteries."
In practice, BESS manufacturers ship containers at ≤30% SoC as standard procedure-both for regulatory compliance and to minimize thermal risk during the 28-65 day sea voyage.
ADR 2025 mirrors the IMDG changes for UN3536:
For inland transport from CEE ports to construction sites, the ADR classification remains Class 9, Classification Code M4. The tunnel restriction rarely affects BESS delivery routes in Bulgaria, Romania, or Poland, as Category E tunnels are uncommon on typical port-to-site corridors.
Prepared by the Manufacturer:
Prepared by the Carrier or Forwarder (as contractual carrier):
Key Document Requirements for UN3536:
Common Field Errors:
Required Documents:
Not Required for Road Transport:
ADR enforcement on CEE roads focuses on:
Polish road inspections (ITD - Inspekcja Transportu Drogowego) are notably thorough. Romanian and Bulgarian inspections occur primarily at border crossings and weigh stations.
BESS containers in the open air. The new regulation forces dangerous cargo into the light of accountability.
The stowage category change to D creates a documentation-reality gap that enforcement has not fully addressed. Some carriers accepted UN3536 bookings during the 2025 transitional period without updating their stowage planning systems. Containers booked as Category A may have been stowed under-deck on vessels departing before 1 January 2026.
Shipments loaded after 1 January 2026 are subject to full Category D enforcement.
The Violation: A booking request was submitted for 40 BESS containers using documentation prepared in 2025 that referenced IMDG Amendment 41-22 and did not include the SW1/SW2 stowage codes.
What Happened: The carrier's DG desk rejected the booking, requesting updated documentation reflecting Amendment 42-24. It took the manufacturer's logistics team 72 hours to issue corrected documents.
The Cost: The shipment missed its intended vessel. The next available DG booking space was 12 days later. The project timeline absorbed the delay, but the buffer for inland transport was eliminated.
The Violation: BESS containers arrived at loading port Shanghai with Class 9 placards on only two sides (front and back), not the required four sides.
What Happened: Carrier flagged the non-compliance. The containers were put on hold until the exporter arranged for compliant placarding to be applied at the terminal.
The Cost: Additional days of export storage fees accumulated. The cut-off for the intended sailing was missed. The containers had to be rebooked for the next week sailing at a higher seafreight rate.
Q: What is the correct UN number for shipping BESS containers by sea?
A: UN3536 (LITHIUM BATTERIES INSTALLED IN CARGO TRANSPORT UNIT) applies to BESS containers where the container itself houses the battery system. This classification became subject to Stowage Category D (on-deck only) under IMDG Code Amendment 42-24, mandatory from 1 January 2026.
Q: Can UN3536 BESS cargo be shipped under-deck on container vessels?
A: No. As of 1 January 2026, UN3536 is classified as Stowage Category D under IMDG Code Amendment 42-24, Section 3.2. This requires on-deck stowage only. Under-deck stowage is prohibited.
Q: How many sides of a BESS container require Class 9 placards?
A: Four sides-left, right, front, and back. This requirement applies to all Class 9 dangerous goods containers under IMDG Code Section 5.3.1. Two-sided placarding is non-compliant and will trigger inspection delays at CEE ports.
Q: What is the State of Charge limit for BESS containers shipped by sea?
A: While IMDG Code does not specify a numeric SoC limit for UN3536, Special Provision 389 requires systems to prevent overcharge and over-discharge. Industry standard practice is ≤30% SoC, aligning with the explicit requirement for standalone lithium-ion batteries (UN3480).
Q: What tunnel restrictions apply to BESS road transport under ADR 2025?
A: UN3536 carries Tunnel Restriction Code (E) under ADR 2025, meaning passage through Category E tunnels is forbidden. Route planning for inland BESS transport must verify tunnel categories along the delivery corridor.
Q: When did IMDG Code Amendment 42-24 become mandatory?
A: Amendment 42-24 became mandatory on 1 January 2026. A 12-month transitional period (1 January 2025 to 31 December 2025) allowed voluntary use of either Amendment 41-22 or 42-24. All shipments loaded after 1 January 2026 must comply with Amendment 42-24.
Next in the series
12 BESS containers from Asia to CEE. The CE certification gap, the routing decision, and how the timeline was recovered when customs flagged a documentation mismatch.
