How do you ship lithium batteries by air, sea or road?

Formula, assumptions, and limits

A lithium battery’s transport class turns on one size figure. For lithium ion and sodium ion it is energy in watt-hours; for lithium metal it is the mass of lithium in the anode. Every mode compares that figure with the same two lines, set out in special provision 188 of the UN Model Regulations and copied into the IMDG Code, ADR and 49 CFR 173.185(c). US highway and rail adds a higher tier, 60 Wh and 300 Wh or 5 g and 25 g, under 173.185(c)(1)(iv).

Formula

where $E$ is the watt-hour rating in Wh, $V_{nom}$ the nominal voltage in V and $C$ the rated capacity in Ah. 49 CFR 171.8 defines it in those words: “Watt-hour (Wh) = ampere-hour (Ah) × volts (V)”. Rated capacity is the capacity the manufacturer measures at its stated load, temperature and cut-off voltage, as IATA’s 2026 battery guidance defines it.

The small cell and battery test is inclusive, because the texts say “not more than” or “may not exceed”:

The first pair covers lithium ion and sodium ion. The second covers lithium metal, where $m_{Li,battery}$ is the sum of the lithium in all the battery’s cells.

Derivation

The rule is a lookup more than a derivation, and the calculator works through it in seven steps:

1. Size: $E$ for the cell and for the battery, or the lithium mass for each. A single-cell battery is a cell, under the closing paragraph of SP 188 and 49 CFR 173.185(a)(1).
2. Small or not: both figures against 20 Wh and 100 Wh, or 1 g and 2 g.
3. UN number from the chemistry and the packing: UN 3480, 3481, 3090, 3091, 3551 or 3552.
4. Route by mode: the IATA packing instruction and section; IMDG or ADR SP 188 or P903; 49 CFR 173.185(c), (c)(1)(iv) or (b).
5. Net mass per package against the route’s limit.
6. State of charge against 30% where the air rules set it.
7. Marks, labels and documents for that route.

Assumptions

• The voltage is the nominal voltage and the capacity the rated capacity, as marked on the case or stated in the UN 38.3 test summary.
• The cell and battery design has passed UN 38.3 testing. Prototypes and production runs of 100 or fewer follow SP 310 or 49 CFR 173.185(e), outside this calculator.
• The batteries are new, not damaged, defective, recalled or sent for disposal.
• Net mass counts the cells and batteries only, not the equipment or the packaging. The 30 kg limit of SP 188 and 173.185(c) is gross mass, so the calculator asks for a weighing of the packed carton once batteries on their own pass 24 kg net, and near the Section IB limit.
• One chemistry per package. A package with both lithium ion and lithium metal batteries carries both UN numbers.

Worked example

A cordless tool ships by air with its battery in the same box. The battery is 14.4 V and 6.8 Ah, four pairs of 3.6 V, 3.4 Ah cells.

• Cell: $3.6 \times 3.4 = 12.24$ Wh, under 20 Wh.
• Battery: $14.4 \times 6.8 = 97.92$ Wh, under 100 Wh.
• Lithium ion, packed with equipment: UN 3481, Lithium ion batteries packed with equipment.
• By air: Packing Instruction 966, Section II. Up to 5 kg net of batteries per package on passenger or cargo aircraft, the tool plus no more than two spare sets.
• 97.92 Wh is over 2.7 Wh, so from 1 January 2026 the battery ships at 30% state of charge or less.
• On the package: the lithium battery mark showing UN 3481. No Class 9 label, no Shipper’s Declaration; a Section II statement on the air waybill.

At 7.0 Ah the same battery is $14.4 \times 7.0 = 100.80$ Wh. That 0.88 Wh moves it to PI 966 Section I: Class 9 label, a Shipper’s Declaration and UN packaging to packing group II.

Edge cases and limits

• Exactly on the line. 20.00 Wh, 100.00 Wh, 1.00 g and 2.00 g are small. 20.02 Wh is not, and a 3.85 V, 5.2 Ah cell is 20.02 Wh.
• 2.7 Wh. The PI 966 Section II charge rule applies “in excess of 2.7 Wh”, so a 2.7 Wh cell is not caught.
• US highway and rail. 49 CFR 173.185(c)(1)(iv) raises the lines to 60 Wh and 300 Wh, or 5 g and 25 g, for packages marked as forbidden aboard aircraft and vessels.
• Hybrid batteries. A battery with lithium metal and lithium ion cells that cannot be charged from outside is lithium metal, with lower small limits of 1.5 g and 10 Wh in total (SP 387; 49 CFR 172.102 SP 388). The calculator does not model hybrids.
• No rounding rule. None of the texts rounds the Wh figure, so the calculator compares the unrounded product and shows two decimals.

Regulatory basis

The air routes follow the IATA Lithium Battery Guidance Document of 1 January 2026, which summarizes the ICAO Technical Instructions 2025-2026 and the IATA Dangerous Goods Regulations (DGR) 67th edition.¹ The sea route is IMDG Code Amendment 42-24, published in full as the annex to IMO Resolution MSC.556(108) and mandatory from 1 January 2026.² US ground shipments follow 49 CFR 173.185 as current on the eCFR.³ European road follows ADR 2025, whose SP 188 matches the IMDG text.⁶

Common errors

1. Wrong voltage. A 10,000 mAh power bank at 3.7 V is 37 Wh; at its 5 V USB output it reads 50 Wh. The rule uses the nominal voltage of the cells, not the USB output.
2. mAh left undivided. 6,800 mAh is 6.8 Ah. A spreadsheet that multiplies 14.4 by 6,800 returns 97,920.
3. A single-cell power bank against 100 Wh. It is judged as a cell, against 20 Wh.
4. Packed with mistaken for contained in. The mark exemption for up to four cells or two batteries applies only to batteries installed in equipment. Packed with equipment always needs the mark and the 1.2 m drop test.
5. Air rules carried to sea. The 30% state of charge limit and the Section II 5 kg and Section IB 10 kg package limits are air rules; on US ground, 5 kg only decides the passenger aircraft marking of 173.185(c)(1)(iii). SP 188 has a 30 kg gross limit for cells and batteries on their own and no charge rule.
6. An e-bike entered as UN 3481. SP 388 makes it a vehicle, UN 3556.

Lithium battery UN numbers by chemistry and packing

The UN number is fixed by two facts: the chemistry and whether the batteries travel with equipment. The proper shipping names below are those of IMDG Code Amendment 42-24.

A package holding equipment with batteries installed and spare batteries beside it is described as packed with equipment (SP 390; 49 CFR 172.102, special provision 181).

Sodium ion batteries are in the IMDG Code, the ICAO Technical Instructions and ADR for 2026, but not yet in the US Hazardous Materials Regulations. 49 CFR 171.7 still incorporates the ICAO Technical Instructions 2023-2024 and IMDG Amendment 41-22. PHMSA’s HM-215R proposal of 10 February 2026 would add UN 3551 and UN 3552.⁸

Air, sea and road rules compared

The same battery can be fully regulated by air and excepted by sea. The table sets out each mode for small batteries, those within 20 Wh and 100 Wh or 1 g and 2 g.

Above the small limits every mode is fully regulated Class 9. By air that is Section IA or Section I: up to 5 kg net per package on passenger aircraft for batteries with equipment, 35 kg on cargo aircraft, and none on passenger aircraft for batteries on their own. By sea and road it is packing instruction P903, packagings meeting packing group II, emergency schedules F-A and S-I and stowage category A at sea. In the US it is 49 CFR 173.185(b).

A US shipper sending UN 3480 or UN 3090 packages by vessel under the IMDG Code adds the passenger aircraft marking or the Cargo Aircraft Only label. The same applies to batteries with equipment over 5 kg net (49 CFR 171.25).⁷

Lithium battery mark and Class 9 label

The lithium battery mark is a rectangle with a red hatched border at least 5 mm wide, 100 × 100 mm, or 100 × 70 mm where the package is too small. It shows a group of batteries, one damaged and burning, above the UN number or numbers (IMDG 5.2.1.10; 49 CFR 173.185(c)(3)).^2,3 It belongs on small-battery packages. A fully regulated package carries the Class 9 lithium battery label instead, a 100 × 100 mm diamond with seven black stripes over the battery symbol.

Two exemptions drop the mark, both for batteries contained in equipment only:

• packages with nothing but button cells installed in equipment, circuit boards included;
• a consignment of two packages or fewer, each with no more than four cells or two batteries installed in equipment.

The mark with a telephone number, the design before Amendment 40-20, may be used until 31 December 2026. In the US the mark in effect on 9 May 2024 has the same end date.

State of charge rules for 2026

State of charge is an air rule. The ICAO Technical Instructions 2025-2026 extended the 30% limit from batteries on their own to batteries packed with equipment, and IATA’s guidance gives the 2026 position:¹

Above 30%, a Section I shipment needs the approval of the State of Origin and the State of the Operator. A Section II battery over 2.7 Wh above 30% leaves Section II: it goes under Section I of PI 966, with the Class 9 label and a Shipper’s Declaration, and needs the same two approvals.¹

The US rule is narrower today. The 49 CFR 172.101 table assigns special provision A100, the 30% limit of 172.102, to UN3480 only. HM-215R, PHMSA’s proposal to harmonize the HMR with the international standards, has not been adopted.^5,8

Shipments this calculator does not classify

Vehicles, damaged batteries, batteries for disposal and prototypes each have their own UN number or special provision, and this calculator does not classify them.

• Vehicles. E-bikes, e-scooters and powered wheelchairs are UN 3556 under IMDG SP 388, and UN3171 in 49 CFR.
• Damaged, defective or recalled batteries are forbidden by air. By sea they go under SP 376 in packing instruction P908, or P911 where they can react dangerously, marked “DAMAGED/DEFECTIVE”. In the US the route is 49 CFR 173.185(f), by highway, rail or vessel only.
• Batteries for disposal or recycling go under SP 377 and P909 by sea and road, and 49 CFR 173.185(d) by US motor vehicle. ADR SP 636 lets collected batteries of 500 g or less each travel to a sorting site with a total of no more than 333 kg per transport unit.
• Prototypes and low production runs of 100 cells or batteries or fewer follow SP 310 and P910, or 49 CFR 173.185(e).