Posted in Batteries

21700 Battery Guide: What You Need to Know

Key takeaways:

  • 21700 battery is short-hand for a rechargeable, lithium ion battery that is 21 mm in diameter and 70 mm long.
  • The big advantage of a 21700 battery over an 18650 battery is the overall energy capacity possible.
  • 21700 batteries are able to reach a maximum capacity of 5000mAh.
  • How to charge 21700 batteries and compatible chargers.

What are 21700 Batteries?

If you’ve been paying attention to the new releases from NITECORE, you probably noticed many of the newest flashlights are powered by 21700 li-ion batteries. In 2019, the LED flashlight industry began the transition to this larger size battery (both physically and in energy capacity) and you can expect to see the trend continue throughout 2020 and beyond. 

Let’s start at the beginning and talk about what the 21700 battery is. Those of you who’ve been around the LED flashlight world probably recognize 18650s as the “gold standard” for flashlight batteries. Long heralded for their compact size and optimal energy density, these lithium ion batteries power some of the brightest, longest running flashlights and are rechargeable to boot!

Much like an 18650 cell, a “21700 battery” is short-hand for a rechargeable, lithium ion battery that is 21 mm in diameter and 70 mm long. As more electronic devices are moving to li-ion batteries as a power source, this size cell first became popular in electric cars like Tesla and electric scooters.

What are the Advantages of 21700 Batteries?

Maximum capacity of 18650 vs 21700 batteries

The big advantage of a 21700 battery over an 18650 battery is the overall energy capacity possible. Battery capacity, measured in milliamp hours or mAh on an 18650 was limited to about 3600mAh because of the size. 

By increasing the overall length and diameter slightly, a 21700 battery is able to reach a maximum capacity of 5000mAh – a 42% increase. For flashlight users, this translates to longer runtimes on a single charge, something that is invaluable for heavy users. And because the diameter is still under 1”, flashlights using these batteries are still capable of fitting in standard 1” weapon mounts and holsters!

21700 vs 18650 Batteries 

You might be wondering, “Can I still use my 18650 batteries?” in the new 21700-powered flashlights. The answer is yes … and no. From a chemistry and voltage standpoint, there is no reason an 18650 battery won’t work in your 21700-size flashlight. Where you will run into trouble though is making a solid connection — 18650 batteries are simply too short and narrow.

We understand that not everyone is ready to switch to the latest technology and some of you have invested some serious money in your 18650 battery collection. If you want to still use your 18650 batteries, look for 21700 battery flashlights that include an 18650 battery magazine like the NEW P12. This special adapter will make up for the extra length and diameter and allow you to use either size battery in your flashlight interchangeably.

Decipher Nitecore Battery Models

battery nomenclature

Nitecore battery models has a defined nomenclature to indicate the type and capacity of the battery.

  1. brand – N is for the Nitecore
  2. composition – L is for Lithium ion
  3. size – 21 is for 21700 while 18 is for 18650
  4. capacity – 50 is for 5000mAh while 40 is for 4000mAh
  5. special type – HP is for high performance which has > 15 A current discharge.
  6. features – i is for i series flashlights while R is rechargeable via the SUB charging port on the battery.

Charging 21700 Batteries

Due to the extra length and diameter of 21700 batteries, some older chargers won’t be compatible with this size battery. Have no fear, there are several options available so you don’t need to sink a lot of money into a new charging solution. Here’s a look at your options.

Buy a compatible charger

This is an ideal choice for heavy users who can’t afford to tie up their flashlight waiting for it to charge or need to charge more than one battery at a time. If this sounds like you, try one of these 21700-ready chargers from NITECORE.

Get a USB-C rechargeable 21700 battery

For travel, casual use or someone wanting to keep their set-up simple, a USB-C rechargeable 21700 is the perfect solution. All you need is a USB-C charging cable and USB power source like a laptop or solar panel, and these batteries can handle the rest.

Flashlights with 21700 Batteries

Ready to get started with the next generation of flashlights? Try one of these 21700-powered flashlights and get ready for longer runtimes and brighter outputs than ever before.

12 thoughts on “21700 Battery Guide: What You Need to Know

    • Hello there! Depending on the type of 21700 battery you get, it can weigh between 2.57 oz to 3 oz. Hope this helps!

  • This seems like the place to explain the 2150HPi. It appears to be the same size as the 21700 batteries and it appears to have contacts both ends so that it will work in any device that takes 21700? But, it has *both* contacts on both ends? So, it can also connect to devices that connect to only one end – like the lite and charger in the MPB21 kit?

    • Hello there! We recommend that you use the NL2150HPi battery for our iSeries Flashlights or the MPB21 kit. If you are looking to use it for other devices, you can always look at the specific Nitecore product on our website and see if the NL2150HPi is listed on the products Compatible Power Sources section. If you have any specific questions about the NL2150HPi battery, please call or email our Customer Service! You can find those both here!

      • Hello – I was hoping to find out if the NL2150HPi battery is compatible with the NWL20 Triple Output Rechargeable LED Work Light?

  • hi i just bought some keeppower 21700 batteries but they measure 77mm long ! why ? they dont fit my charger which assumes 21700 batteries are 70mm long…is there a charger for longer batteries ?

    • Hi David! This is a great question! Slight variations in battery length can occur due to differences in the internal components and construction of the battery. Different manufacturers may design batteries with different internal structures, electrode configurations, and materials, which can affect the overall length of the battery. Additionally, variations in length may also be influenced by factors such as the presence of protection circuits or different types of terminals.

      In terms of a charger, some of our 21700 batteries measure around 77mm long so you’ve come to the right place! If you’re looking for just one charger we would recommend getting the Nitecore Ui1 or if you need more slots we also have the Nitecore UMS4! If you have any more questions please feel free to contact our customer support via our email or call us at (512) 258-6649.

  • Looking to purchase EMR10 and extra batteries for it. Would the NL2150RX, NL2150HPR, and/or NL2150HPi work as extra/replacement batteries?

    • Hi there Jason! You could use either the NL2150HPR or the NL2150HPi as extra batteries for the EMR10! Unfortunately the NL2150RX is too big to fit in the battery slots.

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