Choosing Between 21700 and 18650 Flashlight Batteries: Which is Right for You?

Both the 21700 and 18650 are rechargeable lithium-ion batteries commonly used in flashlights and other devices. Choosing between them will depend on your needs and preferences. Here’s a comparison of these two battery types to help you make an informed decision:

  1. Size and Form Factor:
    • 18650: 18mm diameter, 65mm length
    • 21700: 21mm diameter, 70mm length

    The 21700 is slightly larger, which can mean a bulkier flashlight, but it might also provide more power and capacity due to its size.

  2. Capacity:
    • 18650: Typical capacity ranges from 1800mAh to 3500mAh
    • 21700: Typical capacity ranges from 3000mAh to 5000mAh

    The 21700 generally offers a higher energy capacity, meaning potentially longer runtime for flashlights.

  3. Performance and Power: Generally, the 21700 batteries can handle higher continuous discharge rates compared to the 18650. This means flashlights designed for 21700 might offer brighter outputs for extended periods.
  4. Compatibility: Some devices and flashlights are specifically designed for one type of battery over the other. Always check the compatibility before purchasing. However, some flashlights come with sleeves/adapters allowing for the use of both battery types.
  5. Availability and Price: Historically, 18650 batteries have been more widespread and, in some cases, more affordable due to their widespread use. However, as the 21700 gains popularity, especially in the vaping industry and electric vehicles, its availability is increasing and prices are becoming more competitive.
  6. Safety: Both batteries operate on similar lithium-ion principles, meaning you’ll want to ensure safe charging practices, avoid puncturing or damaging them, and be aware of their temperature during use. Some models have built-in protection circuits.
  7. Device Design: The design of the flashlight (or any other device) will play a role in your decision. A flashlight optimized for a 21700 battery might take advantage of its additional power and capacity to offer better performance.


  • If you’re looking for a more compact design and are okay with potentially shorter runtimes, the 18650 might be for you.
  • If you prioritize longer runtimes, potentially brighter outputs, and don’t mind a slightly larger flashlight, then the 21700 would be a better choice.

Always make sure to do specific research on the flashlight model you’re considering and see which battery it’s optimized for.