Introduction
For A&S Power, understanding 21700 battery specifications is essential when helping OEM customers select the right cylindrical lithium-ion cell for industrial equipment, portable electronics, and custom battery packs. A cell’s capacity, dimensions, nominal voltage, discharge performance, and application requirements all influence the final battery design.
This article explains the key 21700 battery specifications, compares them with 18650 cells, and examines how engineers can select and configure 21700 battery packs for real-world applications. We focus on practical battery engineering considerations rather than relying solely on nominal capacity or marketing claims.
Quick Answer: What Are the Main 21700 Battery Specifications?
A standard 21700 cylindrical lithium-ion cell is identified by its approximate dimensions of 21 mm in diameter and 70 mm in length. Many commercially available cells use a nominal voltage of 3.6 V or 3.7 V, while the full-charge voltage depends on the specific battery chemistry and manufacturer specification.
Typical commercial 21700 lithium-ion cells are available in capacity ranges around 4,000–5,000 mAh, although actual capacities can vary significantly by model and chemistry. The rated capacity, continuous discharge current, charging limits, operating voltage, and safety requirements must always be verified against the individual manufacturer’s datasheet.
Key Takeaways
- Size: The 21700 format generally refers to approximately 21 mm diameter × 70 mm length.
- Capacity: Many commercial cells offer approximately 4,000–5,000 mAh, but available models have different capacity and performance ranges.
- Voltage: Nominal voltage is commonly 3.6 V or 3.7 V for conventional lithium-ion cells. The charging voltage must be confirmed for the selected cell.
- Energy: A single 21700 cell can provide more energy than many 18650 cells, depending on the specific model.
- Applications: Common uses include electric mobility, power tools, energy storage, portable equipment, and custom industrial battery packs.
- OEM Design: Cell selection should be based on current demand, safety requirements, operating temperature, and available enclosure space—not capacity alone.
1. 21700 Battery Specifications at a Glance
The following table provides a practical overview of common 21700 lithium-ion cell characteristics. These figures are format-level reference information or general commercial ranges, not guaranteed specifications for every 21700 battery model.
| Specification | Typical 21700 Lithium-Ion Cell Information |
|---|---|
| Cell format | Cylindrical lithium-ion |
| Approximate diameter | 21 mm |
| Approximate length | 70 mm |
| Common nominal voltage | 3.6–3.7 V |
| Typical capacity range | Approximately 4,000–5,000 mAh for many commercial models |
| Energy per cell | Approximately 14.4–18.5 Wh at 3.6–3.7 V and 4,000–5,000 mAh |
| Full-charge voltage | Commonly 4.2 V for conventional cells; verify the manufacturer’s datasheet |
| Discharge capability | Model- and chemistry-dependent |
| Charging method | Commonly constant-current/constant-voltage charging for conventional lithium-ion cells |
| Common uses | Power tools, electric mobility, portable equipment, energy storage, and battery packs |
The 21 × 70 mm format describes the approximate cell category. Actual manufactured dimensions, including tolerances, insulation, terminals, and protective features, may affect mechanical compatibility. For engineering applications, we recommend using the manufacturer’s official dimensional drawing rather than designing only around the format name.
Reference data from a Samsung INR21700-40T specification and technical research comparing 18650 and 21700 cells illustrate why model-specific data is important.
2. 21700 Battery Size and Dimensions
What Does 21700 Mean?
The name “21700” describes the nominal cylindrical cell format:
- 21: Approximately 21 mm in diameter.
- 70: Approximately 70 mm in length.
- 0: A conventional designation associated with the cylindrical cell format.
The actual dimensions of a manufactured cell may differ slightly. For example, a Samsung INR21700-40T datasheet specifies a maximum diameter of approximately 21.22 mm and a maximum height of approximately 70.30 mm. These dimensions demonstrate why an OEM enclosure needs appropriate mechanical tolerances instead of assuming that every cell will have exactly the same dimensions.
Why Size Matters in Custom Battery Design
The larger physical size of a 21700 cell can provide more internal volume for electrode materials. Depending on the chemistry and construction, this may enable higher capacity or improved current performance compared with a smaller cell. However, larger cells also affect several parts of a battery pack design:
Mechanical Considerations
- Battery pack width and height
- Cell spacing and insulation
- Heat dissipation
- Welding and interconnection layout
Electrical and Assembly Considerations
- Total pack weight
- BMS and enclosure integration
- Terminal configuration
- Operating temperature and safety clearance
When designing a custom 21700 battery pack, we recommend confirming the actual cell dimensions, terminal configuration, operating temperature, and assembly tolerances before finalizing the enclosure.
3. 21700 Battery Capacity and Energy
Capacity is one of the most important 21700 battery specifications. It is normally expressed in milliamp-hours (mAh) or amp-hours (Ah), and it indicates how much electrical charge a cell can deliver under defined test conditions.
A 5,000 mAh cell has a nominal capacity of 5 Ah. However, capacity alone does not determine whether a cell is suitable for a particular application. Engineers must also consider discharge current, operating temperature, cycle life, charging conditions, and the required safety margin.
How to Calculate 21700 Battery Energy
The approximate energy of a lithium-ion cell can be estimated using its nominal voltage and capacity:
For example, a 21700 cell rated at 3.6 V and 5 Ah has an approximate nominal energy of:
The actual usable energy of a battery pack will depend on the operating voltage range, discharge current, temperature, battery management system settings, and application cut-off voltage.
4. 21700 Battery Voltage and Pack Configuration
Many conventional 21700 lithium-ion cells have a nominal voltage of 3.6 V or 3.7 V and a full-charge voltage of 4.2 V. These values are common but must not be treated as universal. The correct voltage limits depend on the cell chemistry and the manufacturer’s technical documentation.
Series Configuration
Cells connected in series increase the total battery pack voltage. For example, a 4S configuration using cells with a nominal voltage of 3.6 V produces an approximate nominal pack voltage of 14.4 V. A 4S pack using cells rated at 3.7 V nominally produces approximately 14.8 V.
Parallel Configuration
Cells connected in parallel increase the available capacity and can increase the pack’s current capability, depending on the cell specifications and interconnection design. For example, a 2P configuration using 5 Ah cells may provide approximately 10 Ah of nominal capacity when the cells are properly matched.
| Model No. | Voltage [V] | Capacity | Thickness [mm] | Width [mm] | Length [mm] | Weight | Certifications |
|
|
25.2 | 25000mAh | 126 | 163 | 77 | 2.7kg | |
|
|
18 | 15000mAh | 85 | 120 | 78 | 1.2kg | |
|
|
18 | 10000mAh | 61 | 120 | 78 | 850g | |
|
|
7.2 | 9800mAh | 40 | 80 | 100 | 400g | |
|
|
25.9 | 15000mAh | 77 | 167 | 181 | 1.7kg | CE |
|
|
3.6 | 50000mAh | 45 | 120 | 75 | 780g | |
|
|
51.8 | 36000mAh | 42.5 | 20.5 | 74 | 10kg | |
|
|
7.4 | 10000mAh | 39.5 | 42.5 | 74 | 230g | CB, UN38.3 |
|
|
10.8 | 9000mAh | 78 | 82 | 129 | 520g | |
|
|
3.7 | 9600mAh | 24 | 44 | 73 | 165g | UN38.3 |
5. 21700 vs. 18650 Battery Specifications
The 21700 and 18650 are both cylindrical lithium-ion battery formats. The main difference is their physical size, although the actual capacity, current performance, cycle life, and safety characteristics depend on the specific cell model.
| Feature | 21700 Battery | 18650 Battery |
|---|---|---|
| Approximate diameter | 21 mm | 18 mm |
| Approximate length | 70 mm | 65 mm |
| Typical capacity | Often around 4,000–5,000 mAh for many commercial models | Varies widely by model and generation |
| Nominal voltage | Commonly 3.6–3.7 V | Commonly 3.6–3.7 V |
| Space requirement | Requires a larger cell arrangement | May be suitable for more compact designs |
| Typical applications | Power tools, electric mobility, energy storage, and high-capacity packs | Portable electronics, tools, industrial equipment, and battery packs |
The 21700 format can offer greater capacity per cell, but the 18650 format remains useful when equipment has tight dimensional constraints or an established cell design.
A peer-reviewed comparison published in the Journal of Power Sources examined the electrochemical, thermal, and geometrical properties of 18650 and 21700 cells. It highlights that cell format affects more than dimensions alone, including thermal behavior and performance characteristics.
Related Resources: 18650 vs 21700 Batteries for Medical Equipment: Complete Design Guide | 18650 vs 18500 vs 21700 Batteries: Differences, Comparison & Selection Guide
6. Common Applications of 21700 Batteries
Due to their capacity potential and cylindrical structure, 21700 lithium-ion cells are used in a range of battery-powered products and energy systems. The suitability of a particular cell depends on the electrical and mechanical requirements of the application.
Electric Mobility
21700 cells can be used in electric mobility products and other systems that require a combination of energy density, discharge performance, and manageable pack dimensions. The final design must consider vibration, thermal management, charging requirements, and protection functions.
Power Tools
Power tools may require high discharge current during startup and heavy-load operation. For these applications, engineers should review the cell’s continuous discharge rating, pulse performance, temperature rise, and cycle-life characteristics.
Energy Storage
21700 battery packs may be used in portable energy storage equipment and other energy systems. Capacity, operating temperature, charging strategy, BMS functions, and long-term reliability are important factors in the design process.
Industrial and Portable Equipment
Industrial monitoring devices, portable instruments, communication equipment, and other electronic products may use custom 21700 battery packs when their space and energy requirements are compatible with the cell format.
7. How to Select the Right 21700 Battery for OEM Projects
When selecting a 21700 cell for a custom battery project, we recommend evaluating the complete operating requirements instead of selecting a cell based only on its advertised capacity.
- Confirm the required voltage: Determine the nominal voltage, operating voltage range, and maximum charging voltage.
- Calculate the energy requirement: Estimate the required capacity based on load power, operating time, and system efficiency.
- Check current demand: Review continuous current, startup current, pulse current, and possible overload conditions.
- Evaluate physical space: Confirm cell dimensions, pack layout, insulation, wiring, connectors, and enclosure tolerances.
- Design the protection system: Select an appropriate BMS or protection circuit based on the series and parallel configuration and the application requirements.
- Review safety and compliance: Evaluate the applicable transportation, product safety, EMC, and market-specific certification requirements.
- Verify the cell datasheet: Confirm capacity, resistance, charging conditions, discharge limits, cycle life, and operating temperature using official technical documentation.
At A&S Power, we approach custom battery projects by considering the customer's equipment requirements, battery structure, and intended operating conditions. A 21700 cell is one possible design choice, not a universal solution for every application.
cells. It highlights that cell format affects more than dimensions alone, including thermal behavior and performance characteristics.
8. 21700 Battery Safety and Quality Considerations
A reliable 21700 battery pack requires more than selecting a cell with a suitable capacity rating. Charging control, overcurrent protection, short-circuit protection, mechanical integrity, and thermal management all contribute to safe operation.
For OEM projects, I recommend verifying the relevant cell datasheet and identifying the applicable product and transportation requirements early in the design process. Cell certification and battery-pack certification are not necessarily equivalent, so the complete assembly should be assessed according to its intended market and application.
The U.S. National Institute of Standards and Technology (NIST) has published research examining the behavior of 18650 and 21700 lithium-ion batteries under thermal intervention conditions. This type of research reinforces the importance of evaluating cell-specific thermal behavior and safety characteristics during battery system development.
Conclusion
Understanding 21700 battery specifications—including capacity, size, voltage, energy, and discharge performance—is essential for selecting the right cell for an OEM battery project. Although the 21700 format is generally associated with a diameter of approximately 21 mm and a length of approximately 70 mm, the actual performance of each cell depends on its specific chemistry, construction, and manufacturer’s datasheet.
When developing a custom 21700 battery pack, engineers should consider electrical requirements, mechanical dimensions, thermal management, BMS protection, certification, and long-term reliability together. A properly selected cell and carefully designed battery pack can help create a solution that meets the practical needs of industrial and commercial applications.
Need a Custom 21700 Battery Pack?
A&S Power provides OEM and ODM rechargeable lithium-ion battery solutions for industrial equipment, portable electronics, energy storage, and other customized applications. Share your required voltage, capacity, dimensions, discharge current, connector, and application requirements with our technical team.
Get Custom Battery QuoteFrequently Asked Questions About 21700 Batteries
1. What are the standard dimensions of a 21700 battery?
A 21700 battery generally refers to a cylindrical cell with an approximate diameter of 21 mm and a length of 70 mm. Actual dimensions may vary according to the manufacturer, terminal design, insulation, and production tolerances.
2. What is the typical capacity of a 21700 lithium-ion battery?
Many commercial 21700 lithium-ion cells have capacities around 4,000–5,000 mAh. However, the available capacity range depends on the cell model, chemistry, design, and intended discharge performance.
3. What is the nominal voltage of a 21700 battery?
Many conventional 21700 lithium-ion cells have a nominal voltage of 3.6 V or 3.7 V. The nominal voltage and full-charge voltage must be confirmed using the selected manufacturer’s datasheet.
4. Is a 21700 battery better than an 18650 battery?
Neither format is automatically suitable for every application. A 21700 cell may provide higher capacity in some models, while an 18650 cell may be more suitable for compact equipment. The correct choice depends on the application’s electrical, mechanical, thermal, and safety requirements.
5. Can 21700 batteries be used to build a custom battery pack?
Yes. 21700 cells can be configured in series and parallel to achieve the required voltage and capacity. The battery pack must be designed with compatible cells, a suitable BMS, appropriate interconnections, insulation, and required safety testing.
6. How do I calculate the energy of a 21700 battery?
Approximate energy can be calculated by multiplying nominal voltage by capacity in amp-hours. For example, a 3.6 V, 5 Ah cell provides approximately 18 Wh of nominal energy.
7. What should I confirm before ordering a custom 21700 battery?
You should confirm the required voltage, capacity, dimensions, discharge current, charging method, connector, operating temperature, BMS requirements, target market, and applicable certification requirements. The cell’s official datasheet should be reviewed before the final design is approved.
