Concept renderA LiPo battery is a lithium-ion cell packed in a flexible pouch instead of a metal can. LiPo pouches can be made thin and shaped to a product, but they can swell. Cylindrical Li-ion cells such as the 18650 offer more capacity in a rigid can. Coin cells suit very small, low-current devices.
A LiPo battery powers most small wearables, while an 18650 cell powers many handhelds and larger trackers. The names suggest two chemistries. In practice the main differences are packaging, shape and how the cell behaves in a housing. This guide compares pouch, cylindrical and coin cells using cell maker datasheets, then covers swelling, protection, safety standards and how to pick a cell for a wearable or a tracker.
This is an engineering summary. Cell specifications change between revisions, so read the current datasheet for the exact part you plan to use. All sources were read on November 12, 2026.
LiPo vs Li-ion: what is the actual difference?
Both are lithium-ion cells. Renata, a Swiss cell maker, describes lithium-ion polymer batteries, or LiPos, as rechargeable batteries using lithium ion technology. During discharge, lithium ions move from the negative electrode to the positive electrode, and they move back during charging. Renata lists wearables such as smartwatches, headsets and fitness trackers among their uses (Renata lithium polymer batteries, as of November 2026).
The names point to construction:
- Lithium polymer battery (LiPo). The electrodes and electrolyte sit in a sealed, flexible laminate pouch. The cell is flat and can be made in many sizes.
- Cylindrical Li-ion. The electrodes are rolled into a metal can. The name encodes the size. The Molicel 18650 cell in the table below is 18.6 mm in diameter and 65.2 mm high.
- Prismatic Li-ion. A flat, rectangular hard case.
- Coin cells. Small button cells. Some are primary (single use), such as the CR2032. Others are rechargeable lithium-ion coin cells.
Nominal voltage is similar across rechargeable formats: the Renata LiPo pack and coin cell below are rated 3.7 V, and the Molicel cylindrical cells 3.6 V. The Molicel M35A charges to 4.2 V and discharges to 2.5 V (Molicel datasheet, as of November 2026). The Renata LiPo pack charges to 4.2 V and cuts off at 3.0 V (Renata datasheet, as of November 2026). Always use the limits in the datasheet of your own cell.
How do pouch, cylindrical and coin cells compare?
The table lists one example of each format, with figures from each maker's own page or datasheet, as of November 2026. They show the range of each format. None of them is a recommendation.
| Cell | Format | Nominal voltage | Capacity | Size and weight | Source |
|---|---|---|---|---|---|
| Renata ICP501022UPM | LiPo pouch pack with safety circuit | 3.7 V | 80 mAh nominal, 75 mAh minimum | 5.5 × 10.0 × 24.0 mm max, about 2.6 g | Renata datasheet |
| Renata ICR1254 B1 | Rechargeable lithium-ion coin cell | 3.7 V | 72 mAh | 12.2 mm diameter, 5.6 mm high, 1.6 g | Renata product page |
| Panasonic CR2032 | Primary lithium coin cell (not rechargeable) | 3 V | 225 mAh | 20.0 mm diameter, 3.2 mm high, about 2.8 g | Panasonic datasheet |
| Molicel INR-18650-M35A | Cylindrical Li-ion, steel can | 3.6 V | 3,450 mAh typical (12.5 Wh) | 18.6 mm diameter, 65.2 mm high, 48 g max | Molicel datasheet |
| Molicel INR-21700-P45B | Cylindrical Li-ion | 3.6 V | 4.5 Ah typical (16.2 Wh) | 21700 format | Molicel product page |
Energy in watt-hours is nominal voltage times rated capacity. For the 80 mAh Renata pack, that is 3.7 V × 0.080 Ah, or about 0.3 Wh. For the 18650 above, Molicel states 12.5 Wh. That is roughly 40 times the energy of the small pouch, in a cell that weighs 48 g instead of 2.6 g. Watt-hours also decide how a battery ships, so record them early. Our guide to shipping a LiPo wearable under UN38.3 explains why.
Renata's LiPo range shows how small pouch cells get. Its list starts at a 35 mAh cell measuring 3.7 × 10.2 × 19.5 mm (Renata lithium polymer batteries, as of November 2026). Cylindrical cells come in fixed sizes, so the product shape follows the cell.
When does an 18650 battery fit a product?
An 18650 battery is a cylindrical Li-ion cell in a standard size. Molicel's INR-18650-M35A datasheet lists 3,450 mAh typical capacity, 12.5 Wh, a maximum continuous discharge of 10 A, a steel can, and volumetric energy density of 730 Wh/l (Molicel datasheet, as of November 2026). Its larger relative, the INR-21700-P45B, lists 4.5 Ah (16.2 Wh) and a maximum discharge current of 45 A (Molicel P45B, as of November 2026).
Those numbers suit products with room for a cylinder: handheld scanners, larger trackers, desk devices and battery packs. They do not suit a ring or a slim band. A cylinder also wastes space in a flat housing, because the corners around it stay empty. The steel can is the main benefit. It keeps its shape, resists puncture and makes the mechanical design predictable.
Charge temperature differs between cells too. The Molicel M35A allows charging from 0 °C to 60 °C (Molicel datasheet, as of November 2026). The Renata LiPo pack allows 0 °C to 45 °C (Renata datasheet, as of November 2026). The charger has to follow whichever cell the product uses.
Why do lithium polymer battery pouches swell, and how do you design for it?
A pouch cell has no rigid case. As the cell ages, and faster if it is overcharged, overheated or deeply discharged, its electrodes change and some gas can form. The soft pouch then grows thicker. A steel can holds its shape under the same conditions, though it still has limits.
In a sealed wearable, a pouch that grows can push on the display, the board or the back cover. A product that fits perfectly on day one can crack or open a seam later. Plan for this in the mechanical design:
- Ask the cell maker for the cell thickness at the start of life and at the end of its rated cycle life. Design the pocket to the larger number. Do not guess a percentage.
- Leave a gap or a compressible pad above the pouch. Avoid hard ribs that press on one spot.
- Keep sharp edges, screws and solder joints away from the pouch surface.
- Keep the cell away from heat sources such as the charger IC, the radio power amplifier and the wireless charging coil.
- Set the charge voltage and temperature limits from the datasheet, and do not raise them to gain runtime.
Cycle life is part of the same picture. Renata rates the ICP501022UPM at more than 80% of minimum capacity after 500 cycles at 0.5 C charge and discharge (Renata datasheet, as of November 2026). If the product will see more cycles than the rated number, ask the maker what to expect.
What protection and charging does each cell need?
Every rechargeable lithium cell needs limits on voltage, current and temperature. Where those limits live depends on the cell.
- Protection circuit. Many small LiPo packs include one. The Renata ICP501022UPM is sold as a pack with a safety circuit (Renata datasheet, as of November 2026). Bare cylindrical cells are often supplied without one, so the product adds it on the board or in the pack.
- Charger settings. The Renata pack uses constant current then constant voltage at 4.2 V, with a normal charge current of 0.5 C (40 mA) and a maximum of 1.0 C (80 mA). The Molicel M35A lists 1.7 A standard and maximum charge current. Each charger must be set to its own cell.
- Temperature sensing. A thermistor on or near the cell lets the charger stop outside the allowed range.
- Discharge current. A cellular tracker draws short, high peaks. Check that the cell's maximum discharge current covers them with margin, and add bulk capacitance if needed.
Primary coin cells need different care. Panasonic lists the CR2032 continuous drain at 0.2 mA (Panasonic datasheet, as of November 2026). A Bluetooth radio draws pulses well above that, so check the pulse behavior with the cell maker before you commit. For a full checklist of cell, pack and charger safety items, see the smart ring battery safety standards checklist. For how regulator choice affects battery life, see LDO vs buck converter.
Which safety standards and shipping rules apply to lithium cells?
The main international safety standard for portable rechargeable lithium cells is IEC 62133-2:2017. It specifies requirements and tests for the safe operation of portable sealed secondary lithium cells and batteries under intended use and reasonably foreseeable misuse. That edition, published February 7, 2017, added coin cell requirements and mechanical vibration and shock tests. Amendment 1 was published on July 15, 2021, and the current consolidated version is IEC 62133-2:2017+AMD1:2021 (IEC webstore, as of November 2026). Renata states that the ICP501022UPM is IEC 62133 certified (Renata datasheet, as of November 2026).
US retailers and test labs may also ask about UL standards for lithium cells and battery packs, such as UL 1642, Lithium Batteries, edition 6, and UL 2054, Household and Commercial Batteries, edition 3 (UL 1642 and UL 2054 catalog pages, UL Standards & Engagement, as of November 2026). Ask your test lab which standards and editions apply to your product and sales channels.
Shipping is a separate set of rules. Under US hazardous materials rules, each lithium cell or battery must be of a type proven to meet the UN38.3 tests, and the manufacturer and later distributors must make a test summary available. Prototypes shipped for testing and low production runs of no more than 100 cells or batteries a year are excepted from that testing, under stricter packaging rules (49 CFR 173.185, as of November 2026). The rules also depend on watt-hours and on whether the battery ships inside the device. See shipping a LiPo wearable: UN38.3 and watt-hours and shipping device samples with lithium batteries by air to the US.
How do you pick a cell for a wearable or a tracker?
Start from the housing and the power budget. The table gives typical starting points. It is engineering reasoning, and the right cell depends on your current profile and enclosure.
| Device | Typical cell | Why |
|---|---|---|
| Smart ring | Small curved LiPo pouch or a rechargeable coin cell | Space and shape rule out cylindrical cells. Swelling room and heat near skin matter most. |
| Wristband or pendant | Flat LiPo pouch | The pouch can be made thin and sized to the board. Leave room for growth. |
| Bluetooth tag or button | Primary coin cell such as a CR2032 | No charger needed. Check that radio pulses suit the cell, since the datasheet continuous drain is low. |
| LTE or GNSS tracker | Larger LiPo pouch, or an 18650 or 21700 cell when the housing allows | Cellular transmit peaks and long life favor more capacity. A steel can resists swelling but fixes the shape. |
| Handheld or desk device | 18650 or 21700 cylindrical cells | Standard sizes, high capacity per cell and a rigid can. |
Measure the real current profile on a prototype before you fix the capacity. Our guide to testing battery life claims honestly shows how. The battery choice, charger and housing are planned at the gates described in how the engineering gates run.
What should you ask the cell maker?
Send these questions with your first sample request.
- What is the cell thickness at the start of life and at the end of rated cycle life, at our charge voltage?
- Which charge voltage, charge current and charge temperature range does the datasheet allow?
- Is a protection circuit built into the pack, and what are its overcharge, overdischarge and overcurrent thresholds?
- Which IEC 62133-2 or other test reports exist for this exact cell and pack, and who issued them?
- Is a UN38.3 test summary available for the pack we will ship?
- What are the watt-hours of the pack, calculated from nominal voltage and rated capacity?
- What is the minimum order quantity, and how long will this cell stay in production?
Questions about LiPo and Li-ion cells
Is a LiPo battery the same as a lithium-ion battery?
They use the same lithium-ion chemistry family. Renata describes lithium-ion polymer batteries, or LiPos, as rechargeable batteries "using lithium ion technology" (Renata, as of November 2026). The practical difference is packaging: a LiPo cell is a flexible pouch, while common Li-ion cells such as the 18650 sit in a rigid metal can.
Is an 18650 battery safer than a LiPo pouch?
Neither is safe or unsafe by format alone. Safety depends on the cell quality, the protection circuit, the charger settings and how the housing treats the cell. A steel can resists swelling and puncture better than a pouch. A pouch can be sized to the product. Both need protection and tested charging limits.
Can I charge a LiPo battery below freezing?
Check the datasheet for the exact cell. The Renata ICP501022UPM datasheet allows charging from 0 °C to 45 °C and discharging from -20 °C to 60 °C (Renata datasheet, as of November 2026). The charger should read a thermistor and stop charging outside the allowed range.
Can a CR2032 coin cell be recharged?
No. A CR2032 is a primary lithium manganese dioxide cell. Panasonic lists it at 3 V and 225 mAh nominal (Panasonic datasheet, as of November 2026). If the product must recharge, use a rechargeable lithium-ion coin cell or a small LiPo instead.
How can Duobay help choose the battery for my device?
Duobay develops custom devices with a Shenzhen engineering team that covers electronics, firmware, enclosure, app and test, so the cell, charger, protection and housing are planned together. Source files are assigned to you at every paid gate, and firmware source and the SBOM are delivered. Initial calls are free, and we do not publish prices. Tell us about your device.
If you are choosing a battery for a wearable or tracker and want it planned with the charger and housing, tell us about your device.
Sources. All pages accessed November 12, 2026. Re-read the current datasheet for your exact cell before you rely on any figure.
- Renata, Lithium Polymer batteries product range (link)
- Renata, ICP501022UPM datasheet, Rev. V02, August 2019 (link)
- Renata, ICR1254 B1 rechargeable lithium coin cell (link)
- Molicel, INR-18650-M35A product data sheet, version 1.4 (link)
- Molicel, INR-21700-P45B product page (link)
- Panasonic Energy, CR2032 datasheet, as of February 2026 (link)
- IEC, IEC 62133-2:2017 webstore page (link)
- UL Standards & Engagement, UL 1642 and UL 2054 catalog pages (UL 1642, UL 2054)
- eCFR, 49 CFR 173.185, lithium cells and batteries (link)
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