What is 21700 battery?
Table of Contents
- Quick Answer
- What are the dimensions and specifications of a 21700 battery?
- What is the internal resistance of a 21700 cell?
- How Does a 21700 Battery Work?
- Comparison: 21700 vs 18650 vs 26650
- What are 21700 batteries used for?
- Are 21700 batteries safe?
- How long does a 21700 battery last?
- How to choose the right 21700 battery?
- Do I need a special charger for 21700 batteries?
Simple Questions
A typical lithium-ion 21700 battery contains a graphite anode, a lithium-metal-oxide cathode (such as NMC or NCA), a lithium-salt electrolyte in organic solvents, a porous polymer separator, and aluminum and copper current collectors inside a steel or aluminum can.
No—21700 and 18650 batteries are not interchangeable because the 21700 cell is physically larger (21×70 mm vs. 18×65 mm) and may have different current and thermal requirements, so compatibility depends on the device’s battery compartment, contacts, and protection design rather than voltage alone.
21700 batteries are generally better than 18650 in applications that allow the larger size because they typically offer higher capacity and higher continuous discharge capability, while 18650 cells remain preferable where space, weight, or existing device compatibility is critical.
No, not all 21700 batteries are flat top—21700 cells are available in both flat-top and button-top designs, and the correct type depends on the device’s contact design and required overall battery length.
For a standard lithium-ion 21700 battery, the commonly accepted minimum cutoff voltage is 2.5V per cell, as discharging below this level can cause permanent capacity loss and safety risks.
21700 batteries do not inherently require protection circuits, but unprotected cells rely on the device or battery management system to prevent overcharge, over-discharge, overcurrent, and short-circuit conditions, while protected 21700 batteries integrate a built-in PCB for safer standalone use in consumer electronics.
The lifespan of a 21700 lithium-ion battery is mainly affected by charge and discharge depth, operating temperature, charge voltage limits, discharge current, storage state of charge, and overall cycle count under real use conditions.
The most widely trusted manufacturers of high-quality 21700 lithium-ion batteries are Samsung SDI, LG Energy Solution, Panasonic (including Sanyo), Sony Murata, and Molicel, all known for consistent capacity ratings, strong safety records, and use in EV, power tool, and industrial applications.
A 21700 lithium-ion battery should be disposed of through a certified battery recycling program or hazardous waste collection site, never in household trash, to prevent fire risk and ensure proper recovery of lithium, cobalt, and other materials.
Quick Answer
21700 battery is a cylindrical rechargeable lithium-ion cell measuring 21 mm in diameter and 70 mm in length, designed to deliver higher capacity and current than an 18650 battery. It typically offers 3000mAh~5000mAh capacity at a nominal voltage of 3.6~3.7 V, making it suitable for high-power and long-runtime applications. Common uses include electric vehicles, power tools, energy storage systems, and high-output flashlights.
What are the dimensions and specifications of a 21700 battery?
21700 battery has standardized dimensions of 21 mm diameter and 70 mm length, which is the origin of its name. Typical specifications include a nominal voltage of 3.6~3.7 V, capacity ranging from about 3000 to 5000 mAh, and discharge ratings that vary from 3C to 15C. Electrical performance, weight, and maximum continuous discharge current depend on the cell chemistry and manufacturer.
What is the internal resistance of a 21700 cell?
The internal resistance of a 21700 lithium-ion cell is not fixed and varies by cell chemistry, design, and manufacturer. In general, it is lower than many 18650 cells and is typically range 5 to 35mΩ, with high-power 21700 cells designed for especially low resistance. Lower internal resistance enables higher discharge currents, reduced heat generation, and better efficiency under load.
How Does a 21700 Battery Work?
21700 battery works by moving lithium ions between the cathode and anode through an electrolyte during charge and discharge, generating electrical energy. Its larger cell size allows more active material and lower internal resistance than smaller cells, supporting higher capacity and current. A built-in or external battery management system (BMS) is used in packs to control charging, discharging, and safety limits.
Comparison: 21700 vs 18650 vs 26650
18650 vs 21700, Which battery has higher capacity and discharge rate?
21700 battery generally has higher capacity and higher discharge capability than an 18650 battery because of its larger size (21×70 mm vs. 18×65 mm). Typical 21700 cells provide 3000~5000 mAh with higher continuous current ratings, while most 18650 cells range from 1200~3500 mAh. As a result, 21700 batteries are favored in high-power and long-runtime applications where thermal and current handling are critical.
What are the disadvantages of using 21700 over 18650?
The main disadvantages of a 21700 battery compared to an 18650 are its larger size and higher weight, which limit compatibility with devices designed specifically for 18650 cells. In tightly packed designs, 21700 cells can also increase thermal management and mechanical design constraints despite their higher performance.
How does a 21700 compare to a 26650 battery?
21700 battery is smaller and lighter than a 26650 battery, measuring 21×70 mm versus 26×65 mm, which allows higher energy density in a more compact format. While both are typically 3.6–3.7 V lithium-ion cells, 26650 batteries often prioritize higher capacity, whereas 21700 cells balance capacity, power output, and thermal performance. Device compatibility is a key difference, as 21700 batteries fit modern EV, tool, and flashlight designs where space efficiency matters.
What are 21700 batteries used for?
21700 batteries are used in applications that require high energy density and high discharge capability. Common uses include electric vehicles, power tools, energy storage systems, e-bikes, and high-output LED flashlights. Their larger format supports longer runtime and improved thermal performance compared to smaller cylindrical cells.
Are 21700 batteries safe?
21700 batteries are safe when properly designed, manufactured, and used within their specified limits. Like all lithium-ion cells, they require correct charging, temperature control, and protection circuits in battery packs to prevent overcharge, over-discharge, and short circuits. Safety ultimately depends on cell quality, device design, and user handling, not the 21700 format itself.
How long does a 21700 battery last?
The runtime of a 21700 battery depends on its capacity, discharge rate, and application load. With typical capacities of 4000~5000 mAh, a single cell can power low-drain devices for many hours, while high-power tools or lights may drain it much faster. In terms of lifespan, most 21700 lithium-ion batteries deliver hundreds of charge–discharge cycles before noticeable capacity loss under normal use.
How to choose the right 21700 battery?
To choose the right 21700 battery, match the capacity and continuous discharge rating to your device’s power demand. Verify physical compatibility, charger support, and required protection features, especially for high-current applications. Always select cells from established manufacturers with published specifications and safety data.
Explore the highest capacity 21700 or the highest discharge rate 21700
Do I need a special charger for 21700 batteries?
21700 battery does not require a unique charging chemistry, but it does require a charger that physically supports the 21700 size. The charger must follow standard lithium-ion CC/CV charging with a 4.2 V charge termination unless the cell is specified otherwise. Always confirm the charger’s current rating and compatibility to avoid overheating or incomplete charging.
