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What You Need to Know about Li-ion Batteries & Battery Chargers

As much as we love a good AA or AAA penlight, in order to get the brightest and most powerful outputs, the flashlight industry relies on li-ion batteries to provide the juice necessary. The downside is that li-ion batteries aren’t as widely available as alkaline and niMH/niCd batteries and if you’ve never used them before, can present a bit of a learning curve.

Today’s blog will help you get acquainted with how to shop for the right li-ion batteries for your device as well as introduce you to your options for charging li-ion batteries. Let’s dive in!

Quick Introduction to Li-ion Batteries

Originally developed for use in laptop battery packs, 18650 li-ion batteries are by far the most frequently used battery types in today’s LED flashlights. Only slightly larger than a traditional AA battery, the 18650 has become the gold standard in the flashlight market for its balance of size, output and charging lifespan.

Naming Convention

You might be wondering at why we call these batteries 18650s, and believe it or not, there is rhyme and reason. For all li-ion batteries, the name is composed in the following way:

  • First two digits indicate the diameter of the battery in mm
  • Second two digits indicate the length of the battery in mm
  • The “0” indicates it is a round cell

Based on the above convention, you can see that an 18650 battery is 18 mm in diameter, 65 mm in length and circular in shape. And yes, we do have batteries in all sorts of dimensions! For example, a smaller cell that is quite popular in many everyday carry flashlights is a 16340. Although flashlights using these cells will ultimately be capable of less powerful outputs and have shorter runtimes than their 18650 counterparts, the smaller size is often preferred for everyday use.

Key Specifications

Once you’ve determined the correct size battery for your flashlight, there are 2 other specifications you’ll want to pay attention to.


The capacity of the battery is given in milliamp hours or mAh and is usually listed on the side of your battery. For an 18650 battery, typical capacities will range from 2300 to 3500mAh while a smaller 16340 cell will have capacities in the 500-700mAh range. In general, the higher the capacity rating, the longer runtime you will get from your flashlight while lower capacities will be more budget-friendly.

Discharge Rate

The other specification to be aware of is the max discharge rating. Measured in amps or A, this number indicates the amount of electrical discharge at a given moment.


Perhaps the most important thing you can do to ensure that the batteries you purchase will be compatible with your flashlight is to follow the manufacturer’s recommendations. For instance, most of the time an 18650 battery can be substituted with two 16340 size batteries, but not always. And as mentioned before, some newer flashlights require custom or high drain batteries to reach their full lumen potential.

And if you ever have questions, you can always reach out to our customer service team who will be happy to point you to the correct cell for your flashlight.

Recharging: Your Charger Options

Now that you have the right batteries for your flashlight, let’s take a look at your options for charging.

Internal Charging

One of the most convenient ways to charge your li-ion batteries is with a flashlight capable of charging internally. Many flashlights like the NITECORE MH12GTS or Olight M2R Warrior can be charged via USB cable and power source such as a laptop, AC adapter, or power bank. Not only does this mean you won’t have to take the battery out and potentially misplace it, but you don’t need to carry any other devices.

External Chargers

The downside to internal charging is that it ties up your flashlight, is often a bit slow, and doesn’t allow you to charge multiple batteries at once. If you’ll be using your flashlight on a daily basis or go through batteries often, you may want to consider a dedicated battery charger. There is a wide range of options available from slim, single channel chargers that are great for quick charging a backup battery on the go all the way to 8-bay chargers for heavy duty battery users.

USB Rechargeable Batteries

There’s one final option for charging, and that’s actually using a li-ion battery with a built-in micro-USB charging port. This new innovation eliminates the need for external chargers and is a great compromise to flashlights with internal charging as it won’t tie up your torch while you recharge. And best of all, if you do find yourself with multiple cells to charge at once, these are still compatible with traditional external chargers. You can find USB rechargeable li-ion batteries in 16340, 14500, and 18650 sizes.

Tips for Picking Out a Battery Charger

Battery Dimensions

As much as battery charger manufacturers try to accomodate all of various lengths and diameter batteries on the market, not every battery is going to fit in every charger. To avoid having a battery that’s too long or too wide for the bays, pay close attention to the sizes supported by the charger. This is also a good time to check to see if your charger will support both li-ion/IMR batteries as well as niMH/niCd batteries if you plan to charge those as well.

Charging Speed

Paying attention to the maximum charging speeds a battery charger is capable of will save you a lot of frustration down the road. Often times chargers will advertise the maximum speed for a single slot, but if it is a charger with multiple slots, that max speed will decrease the more batteries are added. Faster charging speeds also come at a premium.

Digital vs. Analog

The battery chargers in our store fall into 2 categories: digital and analog. The analog chargers, while a little better on the wallet, will only have a basic LED display to indicate charging progress. Although you’ll still know when charging is complete and often have a general idea of where it’s at in the process, you won’t get the same detailed information as a digital charger.


Digital battery chargers like the NITECORE D2/D4 or Fenix ARE-A2/A4 have an LCD display that reports key information for each bay including charging speed and remaining charging time. If you’re the kind of person who likes to know exactly what’s going on, you’ll want to grab a digital charger.

Top Charger Recommendations

With all the above information in mind, we understand there’s a lot to choose from. We put together a few top recommendations for both a single battery charging set up as well as solutions for those of you with a lot of batteries to charge.

EDC Setup

Olight UC Magnetic Charger

Why we love it: The UC charger makes for one of the most lightweight and compact charging options around. The magnetic nodes easily attach to virtually any li-ion battery and allow you to recharge with any USB power source available.

Fenix ARE-X1+

Why we love it: This single channel charger is great for keeping your carry minimal without sacrificing the experience of a full-size charger. A bright, LCD screen reports important information throughout the charging process including charging current and remaining time. The ARE-X1+ can also double as a power bank when paired with a charged battery to recharge other devices such as smartphones and tablets.


Why we love it: The NITECORE UI1 single channel charger is a budget-friendly option designed with vaping enthusiasts in mind. Compatible with larger-sized li-ion batteries including 20700 and 21700 cells, this no-frills charger gets the job done quickly and efficiently.

Multi-Battery Solutions

Fenix ARE-A4

Why we love it: Fenix’s fully digital, four-channel battery charger is an excellent choice for those of you who need to rotate through your batteries on a frequent basis. Compatible with a wide range of popular NiCd/NiMh and li-ion battery types, the ARE-A4 includes an easy-to-read LCD display so you can stay on top of your charging progress.


Why we love it: Another 4-bay option, this time from NITECORE, the SC4 is one of the fastest battery charging options available with a max speed of 3A in a single slot. That means you’ll spend less time waiting for your batteries charging and more time getting back to what you love doing.


Why we love it: There’s no doubt, the i8 is for the heaviest of battery users out there. This 8-bay charger is designed to be a mini power station you can keep on your desktop to charge a wide range of li-ion, niMH and niCD rechargeable batteries. There’s also 2 USB ports for charging devices like cell phones and laptops.

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