Li-Po & Cylindrical
Table of Contents
- 1. Why Do Smart Rings Need Specialized Batteries?
- 2. How to Determine the Right Smart Ring Battery Size
- 3. Smart Ring Battery Size and Capacity Comparison
- 4. Does Higher Battery Capacity Always Mean Longer Runtime?
- 5. Understanding 4.2V and 4.35V Charging Requirements
- 6. Why Battery Tab Orientation Matters
- 7. Standard Smart Ring Battery or Custom-Designed Cell?
- 8. What Information Should OEM Customers Provide?
- 9. Frequently Asked Questions
- 10. Find the Right Smart Ring Battery for Your Project
Designing a smart ring requires balancing battery capacity, physical dimensions, electrical performance and the limited space inside a curved enclosure.
Unlike many conventional wearable devices, smart rings have very little room for a rechargeable battery. Cell geometry, thickness, terminal position and charging compatibility can therefore become critical design considerations.
A suitable smart ring battery must fit the available internal space while supporting the device's power requirements, charging system and intended runtime.
This guide explains how OEM manufacturers and product engineers can select curved lithium polymer (LiPo) battery cells, compare available dimensions and capacities, and determine when a customized battery solution may be required.
1. Why Do Smart Rings Need Specialized Batteries?
Smart rings typically integrate sensors, wireless communication circuitry, a processor, charging components and a rechargeable battery into a compact circular enclosure. These components compete for limited installation space.
Conventional rectangular cells may not efficiently fit the available curved compartment. A purpose-designed curved LiPo cell can offer a more suitable geometry when its mechanical profile matches the device structure.
- Curved cell geometry: The profile must match the installation cavity.
- Limited thickness: Cell thickness directly influences internal clearance.
- Capacity requirements: Capacity must support the target operating time.
- Tab configuration: Terminal position and polarity affect assembly.
- Charging compatibility: The selected cell must match the charging system.
A curved LiPo battery is manufactured with a defined geometry. A conventional flat pouch cell should not be assumed to be freely bendable after manufacturing. The required shape should be considered during mechanical design.
2. How to Determine the Right Smart Ring Battery Size
Selection should begin with the device's physical dimensions rather than capacity alone.
| Dimension | Engineering Consideration |
|---|---|
| Thickness (T) | Available clearance inside the ring enclosure |
| Width (W) | Space allocated across the battery installation area |
| Length (L) | Available length along the intended battery placement |
A 1.25 × 7.1 × 31 mm cell is not necessarily interchangeable with a 1.52 × 7.1 × 31 mm cell: the thicker option may exceed the installation clearance.
Maximum dimensions alone do not confirm compatibility. Engineers should also consider the curved profile, sealing area, terminal position, surrounding electronics and assembly tolerances.
- Establish maximum available battery dimensions.
- Define the required curved geometry.
- Reserve space for battery terminals.
- Account for assembly tolerances.
- Provide clearance for installation and cell expansion.
A mechanical drawing or 3D model helps match the cell to the actual device structure.
3. Smart Ring Battery Size and Capacity Comparison
ASOL supplies smart ring battery cells in different thicknesses, widths, lengths and capacity options. The following representative models illustrate the relationship between dimensions and capacity.
Representative Smart Ring Battery Models
| Model | Maximum Dimensions (T × W × L) | Minimum Capacity at 4.2V | Minimum Capacity at 4.35V |
|---|---|---|---|
| 120732 | 1.25 × 7.1 × 31 mm | 17mAh | 19mAh |
| 126825 | 1.25 × 6.9 × 25 mm | 13mAh | 15mAh |
| 150732 | 1.52 × 7.1 × 31 mm | 20mAh | 22mAh |
| 155625 | 1.52 × 5.6 × 25 mm | 12mAh | 14mAh |
| 180732 | 1.80 × 7.0 × 31 mm | 30mAh | 34mAh |
| 220732 | 2.20 × 7.1 × 31 mm | 34mAh | 38mAh |
Technical Notes: The dimensions shown are specified maximum dimensions. Capacity values represent minimum capacities measured under the stated 0.5C discharge test conditions.
The 4.2V and 4.35V columns correspond to charging cutoff voltage conditions associated with the listed capacity values. They are not nominal cell voltages or evidence that the same cell can be freely charged using either voltage. Final selection must follow the exact electrical and mechanical specifications of the chosen version.
What Does This Comparison Tell Us?
Models 120732 and 150732 both have a maximum width of 7.1 mm and length of 31 mm. Model 120732 has a maximum thickness of 1.25 mm, while model 150732 is 1.52 mm. Under the listed 4.2V charging condition, their respective minimum capacities are 17mAh and 20mAh.
This illustrates a common trade-off: additional thickness may allow greater capacity, but only if the enclosure can accommodate it. A higher-capacity cell is not automatically the best choice when its geometry or terminals interfere with other components.
Review the available Smart Ring Lithium Polymer Battery Cells for representative options.
4. Does Higher Battery Capacity Always Mean Longer Runtime?
Higher capacity can support longer operation, but runtime also depends on device power consumption and operating conditions, including standby, sensor measurements, wireless transmission and synchronization.
Estimated Runtime (hours) = Usable Battery Capacity (mAh) ÷ Average Device Current (mA)
This is an initial estimate only. Usable capacity may differ from laboratory-rated capacity because of discharge conditions, temperature, voltage cutoffs, aging and electronic losses. Engineers should evaluate standby and active current, wireless peaks, voltage requirements, temperatures and target time between charges. Prototype testing with the intended electronics is necessary.
5. Understanding 4.2V and 4.35V Charging Requirements
Some miniature LiPo specifications provide different capacities under 4.2V and 4.35V charging conditions. These are charging cutoff voltages, not nominal cell voltages, and do not mean that every cell can safely use either limit.
The correct charging voltage must follow the exact cell version, chemistry and approved electrical specification. Confirm maximum charging voltage, charging current, termination, overcharge protection, charging-management IC compatibility and temperature safeguards before finalizing the circuit.
6. Why Battery Tab Orientation Matters
Battery tabs connect the cell to the device circuit. In miniature rings, terminal position directly affects PCB placement and assembly. Similar cell bodies may use different terminal configurations.
| Model | Available Tab / Folded-Edge Options |
|---|---|
| 120732 | A / B / C / D |
| 126825 | A / B / C / D |
| 150732 | A / B / C / D |
| 155625 | C / D |
| 180732 | C / D |
| 220732 | C / D |
A/B/C/D identify defined terminal and folded-edge variants. Their physical orientation must be confirmed using the corresponding mechanical drawing. Specify terminal position, polarity and assembly orientation during selection.
7. Standard Smart Ring Battery or Custom-Designed Cell?
When to Choose an Existing Model
An existing model is a practical starting point when the installation space and curved profile match, capacity supports the power budget, charging requirements are compatible and the required terminal configuration is available.
When to Consider OEM/ODM Customization
Customization may be appropriate for a different curved geometry, specific dimensions, a different capacity target, customized tab position or polarity, special electrical connections, or project-specific integration. For very small curved cells, protection circuits, temperature sensors or wires may be limited by physical space. Protection requirements should be considered with the device electrical design.
ASOL supplies existing smart ring LiPo models and supports OEM/ODM customization based on specific project requirements. Broader integration options are described in our Custom Battery Solutions.
8. What Information Should OEM Customers Provide?
A well-defined inquiry reduces engineering revisions. OEM customers should provide:
- Device application: Smart ring, wearable sensor or compact electronics.
- Available battery space: Maximum dimensions and curved profile.
- Capacity requirements: Target capacity and operating time.
- Electrical requirements: Voltage range, normal current and peak current.
- Charging requirements: Charging voltage, current and method.
- Terminal configuration: Tab position, polarity and connection requirements.
- Project quantity: Initial samples and estimated production volume.
- Project schedule: Prototype and production timing.
A mechanical drawing or 3D model is particularly useful for curved-cell evaluation.
9. Frequently Asked Questions
What battery type is used in a smart ring?
Many rechargeable smart ring designs use compact lithium-based batteries, including curved lithium polymer pouch cells. The appropriate battery depends on enclosure geometry, capacity requirements and electrical design.
How do I choose the right smart ring battery capacity?
Start with the device’s average power consumption and target operating time. Then compare suitable battery models that fit the available installation space and verify runtime through prototype testing.
Can a smart ring battery be customized?
Yes. ASOL supplies existing curved LiPo battery cells and supports OEM/ODM customization of dimensions, battery geometry and terminal configurations according to project requirements.
Can I charge a 4.2V-rated cell to 4.35V?
Do not assume that this is permissible. The charging cutoff voltage must follow the exact cell specification. Capacity values measured under different charging conditions do not establish interchangeable charging compatibility.
Can a standard flat LiPo battery be bent into a ring shape?
A conventional flat pouch cell should not be bent into an arbitrary shape after manufacturing. Smart ring applications should use a battery designed and qualified for the required geometry.
What information is needed for a custom battery quotation?
Please provide the required battery dimensions, curved installation profile, voltage and capacity requirements, charging method, terminal configuration, expected quantity and available mechanical drawings.
10. Find the Right Smart Ring Battery for Your Project
Selecting a smart ring battery requires balancing geometry, capacity, electrical compatibility and manufacturing requirements. Begin with physical constraints and the power budget, compare suitable existing cells, and consider customization when a different configuration is required.
Explore the Smart Ring Lithium Polymer Battery Cells series, review Custom Shaped Lithium Polymer Battery Cells, or contact ASOL with mechanical drawings, charging specifications, capacity requirements and estimated order quantity.
