Your Ultimate Guide to Explore the 21700 Battery

Part 1. What is a 21700 Battery?

The 21700 battery is a rechargeable cylindrical lithium-ion cell. Its name reflects its size: 21mm in diameter and 70mm in length. Compared to the well-known 18650 battery (18mm × 65mm), the 21700 offers enhanced capacity, higher energy density, and improved power output for high-demand applications like electric vehicles and energy storage systems.

Part 2. 21700 Battery Size

The 21700 battery maintains the classic cylindrical shape of lithium-ion cells but with increased dimensions. A typical 21700 can store up to 5000mAh, while most 18650 batteries store between 2500mAh and 3500mAh. This extra capacity directly improves device run times and discharge performance, making them ideal for power-hungry applications.

Part 3. Chemistry and Structure

21700 batteries typically use lithium-ion technology, though the specific chemistry may vary:

• Lithium Cobalt Oxide (LCO): High energy density, moderate lifespan.

• Lithium Iron Phosphate (LiFePO4): Safer with extended cycle life, but lower energy density.

• Nickel Manganese Cobalt (NMC): Balanced performance, cost, and safety.

Each cell consists of an anode (graphite), cathode, electrolyte, and a separator to ensure safe ion flow and prevent short circuits.

Part 4. Voltage

The operating voltage of a 21700 battery generally ranges between 3.6V and 3.7V. Key voltage points include:

• Fully Charged: 4.2V

• Nominal Voltage: 3.7V (average operational voltage)

• Cutoff Voltage: 3.0V (discharge limit)

Understanding these ranges ensures proper matching with devices and chargers.

Part 5. Weight

The weight of a 21700 battery typically falls between 50g and 70g, depending on chemistry and manufacturer. While heavier than a standard 18650, this increase is offset by improved capacity and longer run times, particularly valuable for electric vehicles and cordless tools.

Part 6. Energy Density

One of the standout benefits of 21700 batteries is their superior energy density, typically ranging from 250 Wh/kg to 300 Wh/kg. In comparison, 18650 batteries typically offer 180-250 Wh/kg. This translates to extended use between charges without increasing battery pack size.

Part 7. 21700 Cell vs 21700 Pack

A 21700 cell is a single battery unit, while a 21700 pack is a group of cells arranged in series, parallel, or series-parallel combinations:

• Series Connection: Increases total voltage.

• Parallel Connection: Increases overall capacity (mAh).

• Series-Parallel: Combines both for custom voltage and capacity configurations.

Battery packs should integrate a Battery Management System (BMS) for safe monitoring of cell voltage, temperature, and charge cycles.

Part 8. Typical Applications

The 21700 battery powers numerous high-demand devices, including:

• Electric Vehicles (EVs): Longer range with high energy storage.

• Power Tools: Enhanced runtime and output performance.

• Flashlights: Extended use for professional and personal lighting.

• E-Cigarettes: Popular in high-wattage vaping devices.

• Drones: Longer flight times and stable performance.

Part 9. 21700 vs 18650 Battery

The key differences between the 21700 and 18650 batteries lie in their size and performance:

• Size: 21700 is 21mm × 70mm; 18650 is 18mm × 65mm.

• Capacity: 21700 typically offers 5000mAh+, while 18650 peaks around 3500mAh.

• Energy Density: 21700 cells deliver higher energy density and longer runtimes.

Part 10. Battery Lifespan

The lifespan of a 21700 battery is typically measured in charge cycles. On average:

• Li-ion 21700: 500 to 1000 cycles

• LiFePO4 21700: 2000+ cycles

Proper usage — avoiding deep discharges and overcharging — along with moderate storage conditions, will extend the battery’s usable life.

Part 11. Charging and Maintenance

To charge your 21700 battery safely:

• Use chargers designed for lithium-ion cells.

• Avoid leaving batteries unattended while charging.

• Store batteries in a cool, dry location.

Maintenance Tips:

• Inspect for damage or swelling before use.

• Clean terminals regularly.

• For long-term storage, maintain a 40-60% charge.

Part 12. About Xiaolu Battery’s 21700 Series

Xiaolu Battery is a trusted manufacturer specializing in customized lithium battery solutions. From Li-ion and LiFePO4 cylindrical cells to high-capacity battery packs, Xiaolu Battery delivers reliable, efficient, and scalable power options for industrial and consumer applications.

Their 21700 batteries are widely adopted for electric vehicles, power tools, lighting equipment, and energy storage systems. With precise engineering and consistent quality, Xiaolu Battery offers tailored energy solutions to meet your exact requirements.