- IMDG Code: no SOC limit for UN3536. But ports and carriers enforce their own limits, and these change. Never assume yesterday's accepted SOC will be accepted today.
- MSK, COSCO, ONE, CMA CGM: SOC at or below 30 percent. HPL, MSC: SOC at or below 50 percent. Always check before booking. The carrier limit overrides the port MSA guidance.
- JT/T 1543-2025 (May 2025): mandatory series/parallel disconnection during transport. Physical disconnection at the BMS level, not just software-disabled. BMS functional verification within 30 days before loading.
- Great Hensen verifies SOC at Qingdao CFS before every UN3536 loading. Over-limit units never leave the warehouse. This has prevented 12 rejected bookings in the past year.
1. What is SOC and why it matters for UN3536 shipping
SOC (State of Charge) is the percentage of remaining electrical capacity in a battery, expressed as a ratio of current capacity to nominal capacity. A battery at 100 percent SOC is fully charged. A battery at 30 percent SOC has 70 percent of its energy discharged.
For UN3536 shipping, SOC matters because of one fundamental risk: thermal runaway. A lithium-ion battery at high SOC contains more stored energy. If a cell fails during transport (due to physical damage, manufacturing defect, or extreme temperature), a higher SOC means more energy available to fuel a thermal runaway event that can cascade through the entire battery system.
This is why carriers and ports impose SOC limits: to reduce the energy available in the unlikely event of a failure. A BESS at 30 percent SOC contains less than one-third the stored energy of the same unit at 100 percent SOC. The industry consensus, supported by testing from classification societies including DNV and CCS, is that SOC below 30 percent significantly reduces both the probability and severity of thermal runaway propagation.
2. IMDG Code position: no SOC limit
The IMDG Code (Amendment 42-24, current as of 2026) does not impose an SOC limit for UN3536 cargo. According to the International Maritime Organization (IMO), the decision to exclude a specific SOC limit for UN3536 was based on the integrated battery management systems present in cargo transport units, which provide system-level safety protections not available in standalone battery shipments. This is different from UN3480, where IMDG Amendment 40-20 explicitly limits SOC to 30 percent for lithium-ion cells and batteries.
The reason for this distinction is technical. UN3536 systems are large, permanently installed battery assemblies with integrated battery management systems (BMS). The IMDG Code, through Special Provision 389, places more weight on the system-level safety design (BMS protection, physical installation, electrical isolation) than on a single SOC number.
However, this IMDG flexibility has created a regulatory vacuum that individual carriers and port authorities have filled with their own rules. The result: a patchwork of differing SOC limits that exporters must navigate.
3. SOC limits by Chinese port MSA
Each provincial Maritime Safety Administration issues its own guidance on SOC for lithium battery DG cargo. These are guidance documents rather than binding regulations, but in practice, they function as de facto requirements: the MSA will reference its guidance during the maritime DG declaration review.
| Port | MSA SOC Guidance | Special Rules | Verification Required |
|---|---|---|---|
| Qingdao (Shandong MSA) | Below 50% | UN3536 cargo handled regularly. Broadest carrier acceptance in China. | Manufacturer SOC certificate + independent test report |
| Shanghai (Shanghai MSA) | 20% to 50% | SOC below 20% may trigger questions about battery health and whether the BMS can accurately measure at very low charge. 7-day advance MSA filing required. | MSA filing receipt + SOC test report |
| Ningbo (Zhejiang MSA) | Below 50% | UN38.3 Test Report mandatory since October 2025. SOC declaration must accompany the UN38.3 report at MSA filing. | UN38.3 test report + SOC declaration |
| Shenzhen (Guangdong MSA) | Below 50% | Overweight units (over 30t) require terminal bearing test with ground pressure of at least 50t per square meter. | Terminal bearing test report + SOC declaration |
4. SOC limits by carrier
Carrier SOC limits override port MSA guidance. If the port MSA says "below 50 percent" but your carrier requires "not exceeding 30 percent," the carrier limit controls. Below are actual booking requirements as of July 2026.
| Carrier | SOC Limit | Additional DG Requirements | Verification Method |
|---|---|---|---|
| MSK | Not exceeding 30% | UN38.3 + SOC certificate + BMS functional test report | Manufacturer SOC certificate with timestamp. Independent verification at terminal. |
| COSCO | Not exceeding 30% | Chinese-language DG declaration + SOC certificate + packing list with battery specifications | SOC certificate from manufacturer. Random terminal inspection. |
| HPL | Not exceeding 50% | UN38.3 + MSDS + SOC certificate. 72-hour advance DG booking. | SOC declaration with BMS screenshot timestamp. |
| ONE | Not exceeding 30% | Full DG documentation pack + independent SOC verification by third-party surveyor | Independent surveyor report (not manufacturer self-declaration). Most stringent. |
| MSC | Not exceeding 50% | UN38.3 + SOC declaration + vessel acceptance letter (per shipment) | SOC declaration. Vessel master acceptance required per sailing. |
| CMA CGM | Not exceeding 30% | Full IMDG DG declaration + SOC certificate. DG surcharge applies. | SOC certificate. Verified during DG documentation review. |
| OOCL | Not exceeding 50% | UN38.3 + SOC declaration + DG acceptance letter | SOC declaration. |
| EMC / YML | Not exceeding 50% | UN38.3 + MSDS + SOC declaration. 14-day advance DG booking minimum. | SOC declaration. |
Most carriers update their SOC limits quarterly. We maintain a current matrix and check before every booking. If you booked a shipment 90 days ago, do not assume the same SOC limit applies today. For the latest carrier-specific requirements, see our sea freight process guide or contact our DG team directly.
5. BMS protection requirements under JT/T 1543-2025
JT/T 1543-2025, effective May 1, 2025, is China's Ministry of Transport industry standard for lithium battery sea transport safety. According to the China Ministry of Transport (MOT), this standard was developed in response to the growing volume of lithium battery exports from Chinese ports, which have increased over 200% since 2020. It is the first dedicated standard of its kind in China and has significant implications for UN3536 BESS shipments.
Four mandatory BMS protections for UN3536
- Over-charge protection: The BMS must prevent any cell from exceeding its maximum rated voltage during transport. Since the battery is not connected to a charger during sea freight, this primarily serves as a fail-safe in case the BMS malfunctions and attempts to balance cells by charging low-voltage cells from high-voltage cells.
- Over-discharge protection: The BMS must prevent any cell from dropping below its minimum rated voltage. This protects against copper dissolution at the anode, which can create internal short circuits.
- Short-circuit protection: The BMS must detect and isolate any external short circuit at the system terminals within milliseconds. The main contactors must open and remain open until the short circuit is cleared.
- Thermal protection: If the BMS includes temperature sensors at the cell or module level (required for systems with more than 10 modules), the BMS must disconnect the battery if any sensor exceeds a safe threshold defined by the cell manufacturer (typically 60 to 70 degrees Celsius for LFP cells).
All four protections must be verified functional within 30 days before loading. The verification test report is attached to the maritime DG declaration.
6. Series/parallel disconnection: what it means and how to verify
JT/T 1543-2025 introduces a requirement that is unique among global lithium battery transport regulations. According to the China Ministry of Transport (MOT), this disconnection requirement was introduced based on safety analysis following multiple container fire incidents linked to lithium batteries at Chinese ports in recent years.: mandatory physical disconnection of series and parallel battery strings during transport.
What this means in practice
In a typical BESS, hundreds or thousands of individual battery cells are connected in series (to reach the required voltage, e.g., 1,500V DC) and in parallel (to reach the required capacity, e.g., 3 MWh). These connections are made through busbars or cables with contactors.
JT/T 1543-2025 requires that during transport, the series and parallel connections between battery strings (groups of cells) must be physically opened. This means:
- Not a software command. A BMS command to open contactors is not sufficient. The physical disconnection must be verifiable by inspection: a visible gap in the busbar, a disconnected cable, or a locked-open manual disconnect switch.
- Reduces available fault current. When battery strings are connected in parallel, a fault in one string can draw current from all other strings. Physical disconnection limits the available fault current to a single string.
- Documented with photographs. The DG packing inspector photographs the disconnection points and includes them in the Container Packing Certificate documentation package.
Verification process
At our Qingdao CFS, the series/parallel disconnection is verified as part of the pre-loading inspection. Our DG-certified inspector:
- Reviews the BESS electrical schematic to identify all series and parallel connection points
- Physically inspects each disconnection point (visual confirmation of open circuit)
- Verifies that disconnected cables are secured and cannot accidentally reconnect during transport vibration
- Photographs each disconnection point and includes the photos in the inspection report
- Issues a disconnection verification certificate signed by the DG packing inspector
7. SOC verification process before loading
Here is the step-by-step SOC verification process we follow at our Qingdao CFS for every UN3536 shipment. This process is the reason we have prevented 12 rejected bookings in the past year.
- Manufacturer SOC certificate (T-14): The BESS manufacturer provides a SOC certificate stating the SOC at the time the unit left the factory. This is the baseline document. We require this at least 14 days before the target vessel departure.
- CFS arrival SOC check (T-3): When the BESS unit arrives at our CFS, we connect to the BMS interface and read the current SOC. This reading is compared to the manufacturer's certificate. Any discrepancy of more than 5 percentage points triggers an investigation: was the unit operated between factory and CFS? Was there a BMS measurement error?
- SOC comparison with carrier limit: The CFS SOC reading is compared against the carrier's limit for the specific booking. If SOC exceeds the carrier limit, the unit is flagged and held at the CFS for discharge. It does not proceed to the terminal.
- Discharge if required: If SOC exceeds the carrier limit, we coordinate with the manufacturer or a local electrical contractor to discharge the BESS to the required level. For a typical 1 to 3 MWh BESS, this takes 6 to 24 hours depending on the discharge rate and equipment available. The U.S. PHMSA has issued similar guidance recommending pre-loading SOC verification for all large-format lithium battery shipments. The SOC is re-verified after discharge.
- Terminal entry SOC declaration (T-2): The final SOC reading is documented on a SOC declaration form, signed by the DG packing inspector, and attached to the Maritime DG Declaration submitted to MSA.
- Pre-loading re-check (T-1): A final SOC check is performed at the terminal DG yard before the container is positioned for loading. This is a quick verification to confirm no change occurred during the 24 hours between CFS departure and terminal loading.
8. Common SOC-related rejection scenarios
Real cases from our operational experience. Names and specific details have been anonymized.
| Scenario | What Went Wrong | Impact | Lesson |
|---|---|---|---|
| Manufacturer self-certification error | Manufacturer certified SOC at 28% at factory gate. Unit was powered on for customer acceptance testing at a logistics yard en route to port. Arrived at CFS with SOC at 42%. | 1-day delay for discharge at CFS. Cost: approximately USD 200 for discharge equipment. | Never trust a factory-gate SOC certificate. Verify at CFS. |
| Carrier policy change mid-booking | Booking confirmed with HPL (SOC limit 50%). HPL updated its DG policy 10 days before departure, reducing UN3536 SOC limit to 30%. Our cargo was at 45%. | 3-day delay: 1 day to rebook with MSC (SOC limit still 50%), 2 days for documentation amendments. | Check carrier DG policies at T-14 and again at T-3. Changes happen. |
| BMS SOC reading inaccurate | BMS displayed 28% SOC. Independent measurement at CFS showed 41%. The BMS had not been calibrated after the last full charge cycle. | 1-day delay for discharge. Manufacturer dispatched a technician to recalibrate the BMS. | Request BMS calibration certificate as part of the pre-shipment documentation. |
9. Temperature monitoring and log requirements
JT/T 1543-2025 requires temperature monitoring at the battery module level for UN3536 systems with more than 10 battery modules. If temperature monitoring is installed, the following applies:
- Pre-loading temperature logs: Temperature readings for the 48 hours before loading must be provided, showing all modules within normal operating range (typically 15 to 35 degrees Celsius for LFP).
- During transport: For shipments with active GPS tracking (standard on all Great Hensen UN3536 shipments), we can also monitor temperature if the BMS telemetry is connected to the tracking unit. This is optional but recommended for high-value BESS cargo.
- Summer season additional requirements: Some carriers require lower SOC limits during June through September, particularly for routes transiting the Red Sea or tropical waters where container interior temperatures can exceed 50 degrees Celsius during daytime. Check your carrier's seasonal policy before booking.
For complete container and packaging specifications including fire suppression requirements, see our UN3536 packaging and container requirements guide.
10. Frequently asked questions
Can I ship a UN3536 BESS at 0% SOC?
Technically, the IMDG Code does not prohibit 0 percent SOC. However, Shanghai MSA specifically flags SOC below 20 percent for additional review. The concern is that deeply discharged lithium batteries may experience copper dissolution, creating internal short circuits that are not detectable by the BMS. Most carriers prefer SOC between 20 and 30 percent for UN3536. We recommend 25 to 30 percent as the practical sweet spot: low enough to satisfy all carrier limits, high enough to avoid deep-discharge concerns.
How often do carrier SOC limits change?
Carriers typically review their DG policies quarterly. Major changes usually coincide with the summer peak season (June) and the post-peak period (November). Minor adjustments can happen at any time. We maintain a real-time SOC limit matrix and verify against each carrier's current DG acceptance policy at the time of booking and again 3 days before vessel departure.
Does JT/T 1543-2025 apply to shipments from all Chinese ports?
Yes. JT/T 1543-2025 is a national industry standard issued by China's Ministry of Transport. It applies to all lithium battery sea transport from Chinese ports, not just specific ports or provinces. Enforcement began May 1, 2025, with a 6-month transition period that ended November 1, 2025. As of 2026, full compliance is expected at all Chinese ports.
Who pays if SOC is over the limit and the shipment is delayed?
Under standard freight forwarding terms, the shipper (exporter) is responsible for ensuring the cargo complies with all DG regulations at the time of delivery to the carrier. If the cargo is rejected due to SOC exceeding the carrier limit, the shipper bears the cost of discharge, terminal storage, rebooking, and any demurrage. This is why we verify SOC at the CFS before terminal entry: it transfers the cost of a SOC issue from thousands of dollars at the terminal to a few hundred dollars at the warehouse.
Need to verify your BESS SOC before shipping?
Our Qingdao CFS provides pre-loading SOC verification for every UN3536 shipment. Send us your cargo specifications and we will confirm the applicable SOC limits for your chosen port and carrier.
Sources and references
- IMDG Code Special Provision 389 (SP389): IMO International Maritime Dangerous Goods Code, Amendment 42-24. IMO IMDG Code
- JT/T 1543-2025 《船舶载运锂电池安全技术要求》: 交通运输部, 2025年1月26日发布, 2025年5月1日实施. 交通运输部公告
- UN TDG Rev. 24 (2025): UN Model Regulations, 24th revised edition, splitting UN3536 into three codes. UNECE TDG
- Ningbo Port UN38.3 Mandatory Requirement: ONE (Ocean Network Express) advisory, October 2025. ONE Advisory, Seatrade Maritime
- UN38.3: UN Manual of Tests and Criteria, Part III, Sub-section 38.3. UNECE Manual of Tests
- PHMSA Interpretation 25-0015 (April 2025): Clarification on UN3536 placarding requirements. PHMSA 25-0015
- Container Statutory Inspection Technical Rules (2025版): 中国船级社, effective October 1, 2025. Referenced from CCS technical notices.
All operational data based on Great Hensen's shipping records: 1,000+ TEU of UN3536 cargo shipped since 2022. Last verified: July 2026.