Shipping Li-Po Wearables: UN38.3 and Wh Limits

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A small Li-Po wearable shipment is usually judged on two checkable things: the watt-hour math and a UN 38.3 test summary. Wh equals nominal volts times amp-hours. 49 CFR 173.185 sets 20 Wh per cell and 100 Wh per battery for the small-battery exception, as of October 31, 2026.

Samples of battery-powered wearables get held when the paperwork does not match the cell inside. Two items you can prepare yourself are the watt-hour arithmetic and the UN 38.3 test summary. This page turns the text of 49 CFR 173.185 into a checklist and a calculation you can rerun for your own cell. If the cell type is still open, LiPo vs Li-ion batteries compares pouch, cylindrical and coin cells.

This is an engineering team's summary of the regulation. It is not legal advice, and it is not a guide to medical devices. The carrier or a dangerous-goods consultant has the final say. The rule text below comes from the 2023 CFR edition on govinfo.gov, accessed 2026-10-31. Regulations change, so check the current text before you rely on it.

How do you calculate the watt-hour rating?

Formula: Wh = nominal voltage (V) × capacity (Ah). A 3.7 V cell at 0.5 Ah is 1.85 Wh. For cells in series, add the cell voltages. For cells in parallel, add the capacities. Then compare with the small-battery exception: the Watt-hour rating may not exceed 20 Wh for a lithium ion cell or 100 Wh for a lithium ion battery (49 CFR 173.185(c)(1)(i), 2023 edition, as of October 31, 2026).

The capacities in the table are made-up examples to show the arithmetic. They are not data for any product. Replace them with the nominal voltage and capacity from your own cell datasheet. If the vendor has not published a figure, the answer is: vendor did not publish it, so measure it on your board.

Inputs: made-up example voltages and capacities (replace them), and the 20 Wh and 100 Wh limits from 49 CFR 173.185, 2023 edition, as of October 31, 2026. Meeting the Wh limits is one condition of the exception. It is not a statement that your shipment is compliant.

What must a UN 38.3 test summary show?

49 CFR 173.185 requires each manufacturer and subsequent distributor of lithium cells or batteries to make a UN 38.3 test summary available. Use the table as a field-by-field check when a summary arrives from your cell supplier. The fields come from the list in 173.185(a)(3) (source, 2023 edition, as of October 31, 2026).

Do prototypes and small batches get an exception?

Paragraph 173.185(e) says low production runs (annual production runs of not more than 100 lithium cells or batteries) and prototype lithium cells or batteries transported for purposes of testing are excepted from the testing and record-keeping requirements of paragraph (a), provided further conditions are met (source, 2023 edition, as of October 31, 2026). That is directly relevant to EVT samples. The conditions are the part that matters, and this page does not reproduce them. Read the full paragraph, and ask your carrier whether it accepts the exception for your shipment.

Air shipments add rules from IATA, which publishes a Battery Guidance Document that it describes as updated (IATA lithium batteries, accessed 2026-10-31). We did not verify air-specific items, so read the current document yourself.

What can go wrong?

These items are engineering reasoning drawn from the rule text above. They are not accounts of any specific company's shipment, and we have no measured results to report.

• The summary describes a different cell. The rule lists the cell description, including model and Wh rating, as part of the summary. If your design later switches to another cell, the old summary no longer matches what you ship.
• The Wh math was never done on the pack. The limits apply per cell and per battery. A series or parallel pack changes the battery figure, so compute both numbers for the pack as built.
• The Wh rating is missing from the outer case. The small-battery exception requires each lithium ion battery to be marked with its Wh rating on the outer case.
• The summary is incomplete. The rule lists specific elements, including results for each test, the UN Manual edition and a signature. A summary missing one of them gives a carrier a reason to ask for more.
• Nobody confirmed the exception applies. Paragraph (e) comes with further conditions. Treating a prototype as excepted without reading them is a guess.

What should you check on your own board and paperwork?

The rule sets the requirements. Only your own cell, pack and shipment records show where you stand. We have not run these on your product, and this page reports no results. Set the pass line yourself for your product requirements and record the basis for it.

The pass line for each row is yours to set from your product requirements, and you should record the basis for it.

What should you decide before you ship samples?

• Which cell model will the sample use, and does the supplier's UN 38.3 summary name that exact model?
• What is the Wh figure per cell and per battery, and where did the inputs come from?
• Which other cell safety test reports does the cell maker hold, and what do they cover?
• Do you rely on the prototype or low-production exception, and who read paragraph (e) in full?
• Is the Wh rating marked on the outer case of each battery?
• Which carrier and mode will you use, and have you read its current lithium battery terms?
• Who at your company owns the shipping documents and keeps copies?
• Do you need a dangerous-goods consultant to confirm the plan?

Planning a battery-powered wearable and want the Wh math and shipping paperwork checked early? Tell us about your device. For how we plan certification and test steps, see how it works.

Primary sources

All pages below were accessed on 2026-10-31. Confirm the current text before you rely on it.

• govinfo.gov, 49 CFR 173.185, 2023 edition (govinfo.gov/content/pkg/CFR-2023-title49-vol2), accessed 2026-10-31.
• IATA, Lithium batteries (iata.org/en/programs/cargo/dgr/lithium-batteries), accessed 2026-10-31.