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Are 21700 Batteries Better Than 18650?

Batteries come in different shapes and sizes. These technological advancements have been powering our electronics since Alessandro Volta made the battery. Physicists and scientists also made different iterations like rechargeable batteries. This kind of battery was first invented in 1859 by a French physicist named Gaston Planté.

Today, countless rechargeable batteries are being made by different companies. With that, a rivalry has spawned that mainly involves the 21700 and 18650 batteries. So, let’s take a closer look at how they differ.

What Are Lithium-Ion Batteries?

Before moving on to the main topic, we need first to understand Lithium-ion or Li-ion. The 18650 and 21700 batteries are both great examples of Lithium-ion batteries. In a simpler definition, lithium ions move from the negative electrode to the positive one through an electrolyte. This movement creates a charge and thus electricity.

The first Li-ion battery prototype was created in 1985 by Akira Yoshino. His design was based on several research papers conducted between 1970 and 1980. This prototype led to creating a commercial model by a collaboration between Sony and Asahi Kasei in 1991.

Li-ion batteries can use different substances for their electrodes. Lithium manganese oxide and lithium iron phosphate are some examples. The most common one is the lithium cobalt oxide (cathode) and graphite (anode). This combo is mainly used in mobile phones, laptops, and flashlights.

Main Differences

Although they are both Li-ion rechargeable batteries, the 21700 and 18650 are different in many aspects. As a starter, the two have flat top and button top designs and can either be unprotected or protected.

They also vary in size. As its name implies, 21700 batteries are 21 mm x 70 mm. In contrast, the 18650 battery is 18 mm x 65 mm. The zero at the end of their names signifies the model of the cylindrical battery. They also have different capacities. As a rule of thumb, bigger batteries have higher capacities.

Energy plays a key role in a battery’s performance. More energy means you can use your flashlight longer. For example, a 21700 battery can store more energy, from 3000 to 5000 mAh. At the same time, its rival has a range of 2000 to 3500 mAh.

The two are mainly used in flashlights, laptops, mobile phones, and electronic cigarettes. However, 21700 batteries are also used in running electric bikes and cars, electric wheelchairs, and power tools.

Another slight difference between the two is their weight efficiency. It’s measured by gravimetric energy density and tells you how much energy the battery generated in proportion to its weight. The 21700’s weight efficiency is in the 218 Wh/kg range, while 18650 is 223 Wh/kg.

Key Features of 21700 Batteries

The main advantage of the 21700 battery is its size. The battery is still below an inch which is still perfect for everyday carry flashlights. Moreover, a 21700 battery like the Fenix Rechargeable 21700 Li-ion Battery has a higher energy density. Therefore, it makes an excellent choice for higher-capacity battery packs.

The battery also has low priming. Hence, new 21700 batteries can be charged quickly and do not need prolonged charging. Furthermore, as it has 42% more capacity than 18650, the 21700 battery can run longer from a single charge. This feature is advantageous to heavy flashlight users like mechanics or cops.

Key Features of an 18650 Battery

Right off the bat, 18650 rechargeable batteries have a good value and have been the most popular lithium-ion battery. Its market value is estimated at around $6238.3 million by the end of 2020. The value is forecasted to soar up to $6980.2 million in 2026.

An 18650 battery like the Fenix ARBL18 High-Capacity is highly effective. Its efficiency is the result of a great balance between its discharge rate and energy. Moreover, as it has been in the market longer, manufacturers have been updating and improving it.

Cons of 21700 and 18650 Batteries

We have established a clear picture of the pros of the two batteries. Now, to balance it out, we need to consider their cons.

Some may go for flashlights with 21700 rechargeable batteries due to their high capacity. The downside to this one is the charging time. The higher the capacity of a battery is, the longer it takes to charge it.

Moreover, the size can reduce a 21700 battery’s cycle life. It will also decrease the safety and adaptability of the battery. Safety hazards will mainly revolve around excessive heating due to a higher capacity. It’s also expensive to manufacture due to its high capacity.

On the other hand, an 18650 battery is more prone to overcharge and over-discharge. Moreover, like other lithium-ion batteries, their capacity will decline in time. Therefore, heavy users will experience a more abrupt decline in their 18650 battery than frequent users.

How to Choose the Best Battery?

There’s a wide variety of batteries in the market right now. Also, different manufacturers give their take on rechargeable batteries like Fenix Store. So, the dense market becomes a problem on our end as consumers. To help you choose the right 21700 or 18650 battery, here are some key points you need to look for.


The first factor is the voltage. Also known as electrical potential, it is the energy that pushes the electrons in the battery. The higher the battery’s voltage, the more work you get but with the same amount of electrons.


The next is the battery’s capacity. The higher capacity a battery has, the longer you can use it. A battery’s capacity is measured by milliampere-hours (mAh). Most manufacturers put it on the packaging or the battery’s wrapper.

Current Rating

Another important factor to check is the battery’s current rating. If a battery has a high current rating, then it can do more and last longer from a single charge.

Final Thoughts

The two batteries go head-to-head in different aspects. Still, a 21700 is a great step up from an 18650. However, you should always remember that the best battery for your flashlight is indicated on the flashlight’s manual. You cannot use 21700 batteries for a flashlight that requires 18650 ones.