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Lithium Ion Flashlight Battery Sizes – What’s the Difference?

If you’re new to the flashlight world, you may be wondering about all these lithium ion batteries, what they are, what mAh stands for, what they’re good for, etc. So in this article, I want to talk about lithium-ion batteries including the different sizes of batteries and what kind of flashlight you should expect with each battery size. So let’s get started.

Lithium Ion Batteries for LED Flashlights

Flashlights can take all kinds of batteries from alkaline to Ni-MH to lithium. Some LED flashlights even have built-in batteries. However, most ultra bright flashlights are going to run on lithium-ion batteries. This is due to the high energy output these batteries have.

Lithium ion batteries are cost-effective due to the fact that they are rechargeable and provide a lot of power for an LED flashlight. So you can see higher outputs and longer run times with lithium-ion batteries.

What Does MaH Mean in Lithium Ion Batteries?

nitecore i4000r tactical flashlight

MAh stands for milliamps per hour and it’s a unit of electric charge. You’ll see a lot of lithium ion batteries advertising their mAh. Basically, the higher the mAh, the longer the run times are going to be. For example, there are 18650 batteries that have 2600 mAh and 3100 mAh.

With a 3100 mAh, you’re going to be seeing a decently longer run time, up to 30% longer. Of course, you have to keep the voltage in mind as well when picking lithium-ion batteries. A lithium-ion battery with a lower voltage and higher milliamps won’t give you as much power as a battery with higher voltage and lower milliamps. 

I recommend purchasing any 18650 battery from reputable brands such as Surefire, Olight, Nitecore, etc. There are brands out there whose batteries claim  to have a higher mAh capacity than they actually do or are really cheap due to the fact that they’re unprotected so you want to look out for that. 

Lithium-Ion Battery Sizes

Let’s talk about battery sizes. Lithium-ion batteries come in a range of sizes with batteries so small they fit into keychain flashlights. Some LED flashlights can take more than one kind of lithium ion battery which is good to know. But this will give you a general idea of the size of the different batteries. I’ll be talking about more common lithium ion batteries in LED flashlights, but there are more sizes than what I’m listing here.

26650 Li-Ion Battery

26650 li ion battery

This is the biggest battery we’re going to be talking about here. This lithium ion battery is quite large and fits in flashlights that some people like to call soda can lights. These LED flashlights are usually not great for everyday carry due to their larger sizes, but they do provide extremely impressive outputs. I’ve seen 26650 batteries with a high mAh capacity of 5000, but there may be higher out there. The Klarus G20 LED flashlight has this battery.

21700 Li-Ion Battery

21700 lithium ion battery

If you’ve been following my site, you may know that this is my new favorite battery. 21700 batteries are extremely compact but provide a lot of power behind them. You can find flashlights that use 21700 batteries in a variety of sizes from everyday carry to larger duty lights. The highest mAh capacity I’ve seen for a 21700 battery is 5000. I’ve made a big list of flashlights that use 21700 batteries if you’d like to check it out. 

18650 Li-Ion Battery

18650 lithium-ion battery

An 18650 li-ion battery is still probably the most popular battery type for LED flashlights right now. They range in mAh capacities, but the highest I’ve seen would be 3500 mAh. They are smaller batteries, perfect for everyday carry flashlights, hand-held flashlights, tactical flashlights and a lot more.

A couple of flashlights that use this battery would be the Fenix E30R EDC flashlight and the Streamlight ProTac HPL tactical flashlight. 

Here is a pretty cool 18650 battery on Amazon that has a built in micro USB charge port. This is newer technology and is great if your light does not have a recharge port or you don’t want to have to deal with a battery charger.

14500 Li-Ion Battery

14500 li ion battery

A 14500 battery is roughly the same size as an AA battery. These are perfect for pocket flashlights and everyday carry flashlights. The highest mAh I’ve seen for a 14500 battery would be 800. The Klarus XT1A runs on a 14500 battery.

16340 Li-Ion Battery

16340 lithium ion battery

A 16340 battery is shorter than the 14500, but a bit wider. It is a very similar size to a CR123 lithium battery. Many everyday carry flashlights and pocket flashlights use this battery. The highest mah capacity I’ve seen with a 16340 battery is 700. A high quality flashlight that use this particular battery is the Fenix E18R pocket flashlight. 

What Kind of Battery Should I Get for My LED Flashlight?

This all depends on the LED flashlight itself. Each battery listed here is a completely different size and not all batteries are going to be compatible with the same light. So some flashlights like the JetBeam KO-02 can take a 21700 battery and an 18650 battery or the Klarus XT11X which can take an 18650 battery or two 16340 batteries.

On the other hand, some lights can only stick with a single battery type. For example, the Klarus G20 can only stick with 26650 batteries. So I would recommend you first and foremost check out the manual and specs to see what batteries your flashlight needs. 

Another aspect to consider would be button top vs. flat top. Depending on the flashlight you have, it may require either a button top battery or flat top battery. On top of that, I have seen many high-end tactical flashlights that can be a bit finicky about which batteries you use with it.

I recommend purchasing batteries from reputable brands because these will be more likely to work in high-end quality flashlights rather than some of the cheaper batteries you can find online.

Pros and Cons of Lithium-Ion Batteries

21700 vs 18650 battery

Before I end this article I want to briefly discuss the pros and cons of lithium ion batteries. Some of the great aspects of these batteries include the fact that they are rechargeable making them economical. Some lithium ion batteries come with a micro USB port or USB-C port so that you can actually charge the batteries directly.

Also, many LED flashlights are rechargeable which means you can charge the li-ion battery directly in the flashlight. Alternatively, you can use battery chargers.

Also, lithium ion batteries bring a lot of power to the light. You can expect higher outputs and longer run times with lithium-ion batteries than with pretty much any other battery.

One downside of lithium ion batteries is the fact that they don’t have the best shelf life. Lithium ion batteries drain slowly over time. This means that you need to charge them every couple months or so to make sure that the battery doesn’t go into deep discharge.

Deep discharge basically means that the battery is at such a low voltage it will not charge up and you can’t use the battery anymore.

However, with so many USB rechargeable batteries and USB rechargeable flashlights, the benefits of using lithium-ion batteries far outweigh the downfalls. It’s extremely convenient to charge up these batteries. Lithium ion batteries are really a great choice for most tactical flashlights.

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