The "21700" battery is a type of rechargeable lithium-ion (Li-ion) battery that is similar in shape to the well-known 18650 battery but with a larger size and higher capacity. The "21700" designation refers to the battery's dimensions:

    21 mm in diameter
    70 mm in length

Here are some key characteristics and details about 21700 batteries:
Characteristics:

    Nominal Voltage: 3.7 volts, which is the same as 18650 batteries.
    Capacity: Typically ranges from 3000mAh to 5000mAh or more, depending on the specific model and brand. This is significantly higher than the capacity of 18650 batteries, which generally range from 2000mAh to 3500mAh.
    Chemistry: Lithium-ion (Li-ion).
    Charge Cycles: Can be recharged hundreds of times, depending on the quality and usage conditions.
    Self-discharge Rate: Lower than NiMH batteries, but still loses charge over time when not in use.

Applications:

    High-Drain Devices: High-drain devices such as e-cigarettes, flashlights, and portable power banks benefit from the higher capacity and energy density of 21700 batteries.
    Portable Electronics: Some portable electronic devices, such as portable audio players, can use 21700 batteries.
    Power Tools: Some high-performance power tools, especially those requiring high power output, may use 21700 batteries.
    Electric Bicycles and Scooters: These batteries are increasingly being used in electric bicycles and scooters due to their high energy density.

Charging:

    Charging: Requires a charger specifically designed for lithium-ion batteries to avoid overcharging, which can damage the battery.
    Discharging: It's recommended to discharge 21700 batteries fully before recharging to maintain optimal performance, although modern batteries are less susceptible to memory effects.

Safety:

    Handling: 21700 batteries should be handled carefully to avoid short circuits or exposure to extreme temperatures.
    Disposal: Dispose of 21700 batteries according to local regulations, as they contain hazardous materials.

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