What’s the Difference Between 18650 Batteries and 21700 Batteries?

Because 18650 batteries and 21700 batteries are similar in size, many people believe that these batteries are interchangeable. However, a 21700 battery is actually a bit bigger than an 18650 battery. Not only this, a 21700 battery is going to provide a higher mAh which means that you'll be seeing longer run times with this battery.

Even though they're similar in size, a 21700 battery is never compatible in an 18650 flashlight. The 21700 battery itself is going to be too big to fit into an 18650 flashlight. However, a 21700 flashlight may be compatible with an 18650 battery. Many Fenix flashlights that run on 21700 batteries are also able to run on 18650 batteries using a specific Fenix battery holder. However, some 21700 flashlights only run on 21700 batteries. If you want to know what batteries your flashlight runs on, refer to its user manual.

21700 USB Rechargeable Batteries

With 21700 batteries, you can find standard batteries or USB rechargeable batteries. The USB rechargeable batteries have a micro-USB or USB type-C port on the battery which allows you to use a micro USB or USB type-C cable to charge the battery. This is a lot more convenient for many users than purchasing a battery charger to charge your lithium-ion batteries.

Sometimes we’re asked if there are things to consider when purchasing either a standard battery or USB rechargeable battery. While many LED flashlights will be able to run on the USB rechargeable battery, it's not a hard-and-fast rule. USB rechargeable batteries typically are slightly longer than the standard version of the battery. For this reason, certain flashlights may not be compatible with a USB rechargeable battery. An example of this would be with the Fenix UC35. While it works with a standard 18650 battery, the USB rechargeable 18650 battery is just a bit too long and it doesn't function well with that battery. This is just some information to keep in mind when you're trying to decide between a 21700 standard battery and a 21700 USB rechargeable battery.

Rechargeable 21700 Flashlights

Because of the battery's lithium-ion chemistry, many 21700 flashlights are rechargeable via micro USB or USB type-C. A rechargeable flashlight allows you to charge the battery directly through the flashlight itself. This cuts out the need for a battery charger which also cuts down on the total cost. While we always recommend having a battery charger because it's a useful tool to have, it's not necessary.

With a rechargeable flashlight, charging the battery is simple and convenient and there aren't many downsides to a rechargeable flashlight. One downside would be that you can’t always use the flashlight while it's charging which means you have to use a backup flashlight if your battery is drained. However, 21700 flashlights have really long run times so you may not be charging the flashlight that often. Rechargeable flashlights certainly have their perks and if you're looking for a rechargeable 21700 flashlights, make sure to browse this section.