UN 38.3 names transport tests for lithium cells and batteries, and which tests apply depends on whether you ship a cell or a battery. IEC 62133-2 covers safe operation of sealed lithium cells. Confirm the test list against the current Manual edition, then review charger protection features and record measurements on your own board.
A smart ring or band carries a small lithium cell. Before you order samples, three questions come up: which transport tests apply, which standards to ask your cell vendor about, and what to check in the charging circuit. This page is an engineering summary for a hardware lead or compliance owner and does not give legal advice.
Sources are listed at the bottom, all accessed on October 31, 2026. One caution first: the UN text we could read is a 2010 working paper that contains bracketed proposed edits. It is not the current published Manual. Confirm every test name and rule against the current edition before you order tests.
Which UN 38.3 tests apply to a cell, a pack or a single-cell battery?
UN 38.3 is the transport testing section of the UN Manual of Tests and Criteria. The table maps what you ship to the tests named in the working-paper text, as of October 31, 2026.
| What you ship | Tests named | Basis | Source |
|---|---|---|---|
| A rechargeable battery (pack) built from cells | T.1 to T.5 and T.7 | Paper text: this applies even when the pack uses previously tested cells. | UN paper, Oct 31, 2026 |
| A single-cell battery with overcharge protection | T.7, in addition to the tests that otherwise apply | The quoted sentence adds T.7 for this case. Ask the lab which base test set applies under the current Manual. | UN paper, Oct 31, 2026 |
Two more points come from the same text. T.1 to T.5 run in sequence on the same sample, while T.6 and T.8 use cells or batteries not otherwise tested. T.1 is an altitude simulation: samples are stored at a pressure of 11.6 kPa or less for at least six hours at 20 ± 5 °C (source, as of October 31, 2026).
What does IEC 62133-2 cover?
The IEC webstore describes IEC 62133-2:2017 as specifying requirements and tests for the safe operation of portable sealed secondary lithium cells and batteries containing non-acid electrolyte, under intended use and reasonably foreseeable misuse (source, as of October 31, 2026). The standard text is paywalled, so this page does not paraphrase its clauses. For how pouch LiPo cells compare with cylindrical and coin cells, see LiPo vs Li-ion batteries.
What should a charging-circuit design review cover?
The list below pairs charger features documented in one public datasheet, the TI BQ25180, with design items that depend on your cell and enclosure. Use it as an example of what to look for. We do not recommend a specific part (source, as of October 31, 2026). For how the charger, protection IC and fuel gauge work together, see battery management systems for small devices.
| Review item | What to check | Basis |
|---|---|---|
| NTC thresholds | Whether the charger offers configurable NTC thresholds with JEITA support, and how your cell vendor wants them set. | TI BQ25180 datasheet lists configurable NTC charging profile thresholds including JEITA support. |
| Charge safety timer | Whether the timer is programmable and what happens when it expires. | Same datasheet: programmable range 180 to 720 min. |
| Fault reporting | Whether watchdog and safety-timer faults reach the firmware and the user. | Design item. Check your charger datasheet. |
| NTC placement | Where the thermistor sits relative to the cell, and whether the charger reads it during charge. | Design item. Depends on your cell and enclosure. |
| Protection circuit | Whether the pack has one, what it covers, and who specifies it. | Design item. It also decides which UN 38.3 row above applies. |
| Swelling clearance | Free space around the cell inside the shell, and how it is measured. | Design item. Depends on your cell and enclosure. |
| State of charge for shipping | The charge level samples ship at, and who sets it. | Ask your cell vendor and freight forwarder. |
What should you test on your own board?
This is a measurement list: what to measure, how to collect it, and what to record. It reports no results.
| What to test | How to instrument or collect | Raw data to record |
|---|---|---|
| NTC tracks cell temperature | Attach a reference sensor to the cell surface and log it alongside the NTC reading during charge and idle. | Both temperature traces with timestamps, charge current, ambient temperature, sensor positions. |
| Charger thresholds act as configured | Warm and cool the board in a controlled chamber or on a bench and watch the charger status and charge current. | Charger register readouts, charge current versus NTC reading, firmware version, threshold settings. |
| Safety timer and fault path | Force a timer expiry and a watchdog fault in a lab setup and watch what the firmware and app report. | Fault flags, time to fault, user-visible message, whether charging stopped. |
| Swelling clearance | Measure the cell thickness at defined points through charge and rest cycles, and the gap to the shell and board. | Thickness readings with date and cycle count, gap measurements, cell lot, enclosure revision, photos. |
| Protection behavior | Apply the fault conditions your protection circuit is specified for, on a bench with current-limited supplies. | Trip and recovery behavior, voltage and current traces, cell vendor specification used. |
| Shipping state of charge | Record the charge level of sample batches as they leave and as they arrive. | Voltage at packing, voltage at receipt, date, carrier paperwork reference. |
What should you ask before you order samples?
- What exactly will ship: a cell, a pack, or a single-cell battery with overcharge protection?
- Which edition of the UN Manual is current, and has the lab confirmed the test list against it?
- Which standards has the exact cell model been tested to, and can the vendor provide the reports, including for IEC 62133-2?
- Who holds the test reports, and are they in your company's name or the vendor's?
- Does the charger have configurable temperature thresholds and a programmable safety timer, and who set the values?
- Where is the temperature sensor relative to the cell?
- How much free space does the enclosure leave around the cell, and how will you measure it?
- At what charge level do samples ship, and who decides?
Questions about small lithium cell safety
Does passing these standards mean the ring is safe?
No. A standard describes tests under defined conditions. Passing it gives you evidence to show a regulator, a carrier or a customer. It does not guarantee your product is safe. This page is an engineering summary and does not give legal advice.
Which UN 38.3 tests does a ring battery need?
It depends on what you ship. The UN text we reviewed says rechargeable battery types, including those composed of previously tested cells, go through T.1 to T.5 and T.7. A rechargeable single-cell battery with overcharge protection also needs T.7. That text is a 2010 working paper with bracketed edits, so confirm against the current edition of the Manual. UN working paper.
What is IEC 62133-2?
Per the IEC webstore, it specifies requirements and tests for the safe operation of portable sealed secondary lithium cells and batteries containing non-acid electrolyte, under intended use and reasonably foreseeable misuse. IEC webstore.
Planning a worn device with a small rechargeable cell? Tell us about your device. For the product category, see health wearable development.
Primary sources
All pages below were accessed on 2026-10-31. Confirm against current editions before you rely on any detail.
- UN, Manual of Tests and Criteria section 38.3 working paper (2010, with bracketed proposed text) (digitallibrary.un.org), accessed 2026-10-31.
- IEC, IEC 62133-2:2017 publication page (webstore.iec.ch), accessed 2026-10-31.
- Texas Instruments, BQ25180 datasheet (ti.com), accessed 2026-10-31.
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