Battery Sizes for Flashlights: How to Choose the Right One?

Last Updated on May, 2024

So you’re out on the market for a NEW flashlight? Or, maybe you’re just CURIOUS!

Flashlights come in various shapes and forms and Batteries for Flashlights come in a varying range of sizes. There are so many options in the market! Depending on YOUR flashlight’s design, the battery size could vary. 

The size of the battery is dependent on the type of battery. Each type of battery comes in varying sizes. 

Quick Summary

Battery size is an important factor to consider when choosing a flashlight.

Lithium-ion batteries are rechargeable and have a higher energy density compared to alkaline batteries.

The 18650 lithium-ion battery is considered the best battery for flashlights due to its reliable protection circuit, lightweight design, and capacity range.

Types of Batteries for Flashlights

Flashlight Batteries on the floor

Alkaline and lithium batteries are the two broader battery types for flashlights. Most flashlights use one of these two types of standard batteries (check the flashlight manual to find which battery is used.)

Lithium-ion batteries are RECHARGEABLE. While all lithium-ion batteries are lithium batteries, not all lithium batteries are rechargeable. The primary composite of these batteries is lithium. 

On the other hand, alkaline batteries use a reaction between Zinc and Manganese Oxide to power the device; in this instance, a flashlight. 

These are considered the most suitable types of batteries for flashlights. 

Whether you go with a rechargeable or a regular battery, the type of battery you use for YOUR flashlight will depend on the flashlight’s design. 

Every flashlight is designed only to use one specific SIZE of battery. So does size matter?

Sizes of Battery for Flashlights: Does Size Matter?

Since you now have an idea of the two broader types of batteries for flashlights, what are considered the best sizes of batteries for flashlights?

With various designs of flashlights in the market, the SIZE of the battery most certainly DOES matter!

The size of the battery will define its properties, such as its lifetime. 

We’ve divided this list based on the two types of batteries, Alkaline and Lithium. 


Batteries that use an Alkaline reaction to produce energy are powered by a reaction between Zinc and Manganese Oxide. 

While battery chemistry governs the performance of the battery, the shelf life of an alkaline battery is 7 to 10 years.

Here are the best sizes for flashlights.


This is considered one of the most common types of batteries (they are used in remote controls.)

Since AA batteries don’t have the most remarkable longevity, opting for a rechargeable option is considered the wiser choice (rechargeable batteries are better for the planet!)

The size of a AA battery is 49.2–50.5 mm (1.94–1.99 in) in length, including the button terminal—and 13.5–14.5 mm (0.53–0.57 in) in diameter.

Flashlights in the past relied heavily on AA. This was once considered the primary size of battery for flashlights.

Alkaline Batteries on the table

Being the most common battery type in the WORLD, AA is readily available in the market and easy to find. With a shelf life of 5 to 10 years, AA batteries are GREAT for flashlights.

Dual-cell AA light has sufficient brightness (enough to see in the dark.) AA has a capacity over 2500 mAh. 

Check out the best aa flashlights here.


The smaller cousin of the AA battery, the AAA battery is yet another favorite choice of batteries for flashlights. 

AAA batteries are 10.5 mm (0.41 in) in diameter and 44.5 mm (1.75 in) in length, including the positive terminal button, which is a minimum of 0.8 mm (0.031 in).

The smaller size of this battery means more miniature flashlights. 

This is one of the best batteries for flashlights. The lightweight size makes them a perfect fit for small flashlights.

Though non-rechargeable AAA batteries have a lower capacity – 860 to 1200 mAh – many flashlights, use this battery size. 

***Buy batteries that are rechargeable. They will save you a lot of money in the long run and save the planet too.

Lithium Batteries

Lithium batteries are too a POPULAR choice of batteries for a flashlight. Lithium batteries have more capacity in comparison to alkaline ones. They can store more energy. 

As a result, lithium batteries have been slowly capturing the flashlight market. They have a high energy density making them the more advanced type of battery for flashlights.

26650 – Lithium Ion

This is one of the larger types of batteries for flashlights and offers high energy output. High-powered flashlights need a little more juice than regular flashlights.

Hence, this battery is mainly opted for high-grade flashlights. (Max capacity of 5200 mAh.)

26650 has a diameter of 26.5mm and comes at a length of 68.2mm.

This size of battery provides higher voltage compared to other batteries. High-output flashlights require batteries that won’t immediately exhaust, making the 26650 a GREAT choice!

Lithium Batteries in the box

Plus, this lithium-ion battery is RECHARGEABLE!

21700 – Lithium Ion

This smaller, more compact battery is used in many flashlights. This lithium-ion battery is too RECHARGEABLE and is a smart choice for a flashlight battery.

This lithium-ion battery has excellent capacity for size (4000 to 5000 mAh), and we all know rechargeable batteries are better! 

Flashlights that use 21700 come in varying sizes and performance grades. 

This flashlight battery is 21mm in width and 70mm in length. Compared to other batteries in the market, 21700 is small but mighty. Though it isn’t the smallest battery on this list, it is an ADVANCED lithium battery with GREAT performance and reliability.

14500 – Lithium Ion

Lithium-ion batteries are great because they are rechargeable. All you need is a couple of sets of batteries (and these batteries have great charging capacity.)

14500 is of the better rechargeable lithium batteries on the market. It’s roughly the same size as an AA battery. Many flashlights in the market, both big and small, use the 14500 battery. 

Flashlight batteries need good capacity. Otherwise, you would have to keep changing batteries, which can be annoying. 

This battery’s capacity is good (1115 mAh.) Some high-grade flashlights in the market use 14500 as the designated battery. (Though rare)

The dimensions of this battery are 49.2mm in length and 13.5mm in diameter.

16340 – Lithium Ion

This battery is designed to be small. It is one of the smaller batteries on this list. Many everyday flashlights and pocket flashlights rely on this battery. 

Different batteries have different sizes, and the size of this battery is convenient compared to others in the market. 

34mm in width by 16mm in length, this battery has a GOOD capacity (880 mAh.)

This battery has low voltage protection and is even used in various medical devices.

flashlight Batteries

Lithium-ion batteries are rechargeable, and this model of lithium-ion batteries is PERFECT for flashlights!

18650 – Lithium Ion

This is considered one of the most POPULAR batteries for LED flashlights. Though the capacity range varies, these are protected batteries with a protection circuit to prevent an external charger from overcharging them. (These are the same batteries used in Electric Cars)

Protected batteries are better as they are more reliable. 

As the name suggests, the 18650 battery is 18mm wide and 65mm long.

With a capacity range of 2,300 to 3,600 mAh, there are options for both everyday flashlights and high-grade ones. 

18350 – Lithium Ion

This size of the battery is fast becoming the best choice of batteries for custom flashlights. All other batteries, designed to function with CUSTOM flashlights, DO NOT compare to the 18350. This is why they are fast becoming the popular choice for custom flashlights. 

This too is a lithium-ion battery which means it can be recharged. 18350 has a capacity of 1200 mAh. 

Though it isn’t the battery with the highest capacity, it gets the JOB done!

This flashlight battery has enough power and juice to last you a while. Plus, it’s rechargeable, so you won’t have to keep buying new ones!

Checkout the best 18350 flashlights we tested and reviewed.

10180 – Lithium Ion

This battery has become ever so popular for flashlights, not because of capacity. The battery only has a 100 mAh capacity. However, the size of this battery is petite.

It is 10 mm in diameter and 18 mm long (button cells). 

The fact that it is rechargeable is what makes it great! The small size appeals to many buyers regardless of the low capacity. 

If this battery were non-rechargeable, it would completely lose its appeal. 

These batteries are primarily used in neck lights and key chain lights (small.)

flashlight Batteries


Commonly referred to as 123 batteries, this is yet another standard size of battery good for flashlights. (They are popularly used in security alarm systems.)

As you can tell from their use in security alarm systems, this is a RELIABLE battery type. The lifetime of the battery is excellent, and the capacity at 1500 mAh is sufficient to power almost any flashlight. 

This battery is 17 mm wide and has a height of 34.5 mm. You should easily be able to pocket a flashlight that uses this battery. It has an excellent balance of power and size.

The Other Type – NiMH Batteries

Apart from lithium and alkaline batteries, which are the most popular types of batteries used for flashlights, there is one, in particular, that should be included on this list. 

NiMH batteries use an anode of hydrogen-absorbing alloys (MH), a cathode of nickel hydroxide (Ni(OH)2), and a potassium hydroxide (KOH) electrolyte. 

They come in various sizes: AA, AAA, C, D, and 9V. 

D batteries are considered the most preferred NiMH battery for flashlights, though flashlights in other sizes of NiMH batteries are available in the market.

Which Battery is Best for Flashlights? (Size)

The lithium-ion 18650 battery is the best for flashlights.

Not only is it RECHARGEABLE, but these are also protected batteries that prevent damage to the battery due to overcharging. 

They are so reliable that they are even used in ELECTRIC CARS. 

This is because protected batteries are more reliable (whether it be for an electric car or a flashlight.) 

The lightweight design of the battery means you can find a flashlight that works on this battery that would even fit in your pocket. 

However, options are available with a capacity range of 2,300 to 3,600 mAh. If you want a more high-performance flashlight, you can find one that uses this battery! 

Related article: How Long Do Flashlight Batteries Last?

How to Choose a Flashlight Based on Battery Size?

different size Flashlight Batteries on the table

Battery size can be an essential factor when searching for a flashlight in the market. The size of the battery will define how big your flashlight will be and the strength of light illumination. 

The choice of the flashlight is up to you. Only you know where you will be using your flashlight.

However, a few things remain integral in choosing batteries for all flashlights.

Choosing a RECHARGEABLE battery will save you a lot of time and money. Hence, regardless of the battery’s size, try to ensure that the battery is rechargeable. 

Another thing that should be considered is the battery’s capacity, which will define the LONGEVITY and POWER of your flashlight. 

You also want to choose a PROTECTED battery when choosing rechargeable batteries. Batteries that don’t have a protection circuit could easily malfunction and drain due to overcharging. 

Though the size of the battery does matter, there are other parameters that you should take into consideration. While one battery may have a low capacity, the other might be perfect for your needs.

Hence, look into the specifications of the flashlight and the battery used to make an informed and wise purchase. 

Related article: Are these flashlight batteries recyclable?


There sure are many great sizes of batteries for flashlights. It was back in the day when EVERY flashlight ran on AA batteries. 

Now, there are better batteries in the market, those that offer better results. 

The battery size (model type) of a flashlight defines the power and the battery’s longevity. 

All the batteries on this list are good batteries to use in flashlights; but which is the best? The 18650, of course, used in even Electric Cars.


The 18650 battery is widely recognized as the best option for flashlights due to its high capacity and dependability.

No, not all flashlight batteries are rechargeable; the type of battery used must be checked to determine if the flashlight is compatible with rechargeable batteries.

A battery’s capacity is the amount of energy it can store, with higher capacity resulting in longer battery life.

AA and AAA alkaline batteries are suitable for use in flashlights.

The 18650 battery has a diameter of 18 mm and a height of 65 mm.

Was this article helpful?

Photo of author
Dillon Morrison
I have been involved in the flashlight community since 2007. My brother has a flashlight shop from where I have tested and reviewed more than 600+ different types of flashlights. You can find more about me here.

Leave a Comment