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18650 vs 21700 batteries

18650 versus 21700 batteries

We often get asked questions about the differences between the most common battery types. Hence this topic! To give more information about this matter. In this topic we will talk about the main differences between the two most popular battery types for flashlights. The 18650 and the 21700 batteries. As such you can easily decide which battery type will suit you best after reading this topic.

Difference in capacity of the 21700 and the 18650 batteries.

The main difference between the 21700 and the 18650 batteries is the size. Because the 21700 battery is a lot bigger than the 18650 it also has more capacity. The maximum capacity of an 18650 battery is namely around 3500 mAh, while the 21700 battery can produce up to 5000 mAh. More capacity, of course, means more burning hours. As such the 21700 is perfect for long-term use if you cannot charge your battery in between. Think, for instance, of a police officer who needs to handle traffic all night. Depending on the type of light you use, you need to pay attention to the brightness of your light to get through the night, when using an 18650 battery. This will be a lot easier with 21700 batteries.

More room more power

In addition to the difference in capacity the larger size of the 21700 is also an advantage. Because it is larger there is more room to reinforce the cooling and power characteristics of the battery. 21700 batteries namely have a capacity of up to 1400 watts. The 18650 stops at 800 watts. The difference in capacity ensures that the devices that use a 21700 battery have more power. A flashlight with a 21700 battery will therefore burn longer and brighter than a flashlight with a 18650 battery.

Example of the difference in power and capacity

Below a good example of the difference between the two types of batteries. We put this to the test with the Fenix HT18 hunting flashlight, 1500 lumens. We used this flashlight because it easily supports both type of batteries with the help of an insert.

Light modes for the Fenix HT18 with a 21700 Li-Ion battery

  • Turbo: 1500 lumens, burn time of approx. 1:40 hours*
  • High: 500 lumens, burn time of approx. 4:15 hours
  • Medium: 150 lumens, burn time of approx. 20:15 hours
  • Low: 30 lumens, burn time of 61 hours
  • Stroboscope: 1500 lumens

Light modes for the Fenix HT18 with an 18650 Li-Ion battery

  • Turbo: 1100 lumens, burn time of approx. 1:40 hours*
  • High: 500 lumens, burn time of approx. 2:15 hours
  • Medium: 150 lumens, burn time of approx. 14:10 hours
  • Low: 30 lumens, burn time of approx. 53 hours
  • Stroboscope: 1100 lumens

*The burn time of the highest light mode is calculated at the moment the lamp is switched on in the highest mode. After 2-3 minutes, the light automatically switches to a lower mode due to the temperature regulation.

Advantages of the 18650 batteries

When you take all information listed above into account it looks like the 21700 battery is superior. On paper this is true, but the 18650 remains a strong alternative. An 18650 battery is a little more compact and lighter. The 18650 battery is also more affordable. The amount of flashlights that can handle an 18650 battery is bigger and the 18650 battery is a lot more affordable than its bigger brother. In terms of power and capacity, the 18650 battery is more than enough for the average use of a flashlight.


If you are looking for a good rechargeable battery for your flashlight we have got you covered. Whether you go with the larger 21700 or the smaller 18650 battery. We have a wide selection of both of them. Find the right battery on our battery page.