The Facts About Flashlight Batteries: 18650 and 21700

Flashlights are essential tools for outdoor enthusiasts, hikers, campers, and anyone who needs a reliable source of light in the dark. But to get the most out of your flashlight, you need the right battery. This article will cover everything you need about 18650 and 21700 batteries, two of the most popular bright, heavy-duty flashlight options.

21700 battery for flashlights

What is a 18650 Battery?

A 18650 battery is a cylindrical rechargeable lithium-ion battery that measures 18mm in diameter and 65mm in length. These batteries are commonly used in high-performance flashlights, laptops, and other electronic devices that require a lot of power. The key advantages of using 18650 batteries in flashlights include their high energy density, low self-discharge rate, and long lifespan.

Compared to other types of batteries, such as alkaline and lithium-ion, 18650 batteries offer a higher capacity and voltage, which means they can provide more power to your flashlight for a more extended time. In terms of equivalence, one 18650 battery is equivalent to about three AAA batteries or one 123A battery.

How Long Do 18650 Batteries Last?

The lifespan of a 18650 battery depends on several factors, including its capacity, usage, and storage conditions. In general, a 18650 battery can last between 300 and 500 charge cycles, which means it can be recharged and discharged many times before it loses capacity.

A flashlight's runtime of a 18650 battery depends on several factors, including the brightness level and the type of flashlight. In general, a 18650 battery can provide between 1 and 4 hours of runtime on high mode and up to 100 hours on low mode.

To extend the lifespan of your 18650 batteries, it's crucial to avoid exposing them to extreme temperatures or humidity and to store them in cool, dry conditions.

Storing 18650 Batteries

Storing 18650 batteries properly is crucial to ensure their longevity and performance. Avoid exposing your batteries to direct sunlight, heat, or moisture when storing them. It's also essential to store them at a partial charge rather than fully charged or fully discharged.

Charging 18650 batteries to 100% and leaving them sitting for an extended time can cause them to lose capacity and degrade more quickly. Instead, keep your batteries at a 50% charge level when storing them for an extended time.

What is a 21700 Battery?

A 21700 battery is a larger, more powerful rechargeable lithium-ion battery that measures 21mm in diameter and 70mm in length. These batteries are relatively new to the market but are quickly gaining popularity due to their high energy density and long lifespan. They're also becoming more common in high-performance flashlights such as Imalent MS12 Mini - a 65,000 lumens flashlight. 21700 also offers a higher capacity and voltage than 18650 batteries.

Compared to 18650 batteries, 21700 batteries offer a larger capacity and can provide more power to your flashlight for a longer time. In terms of equivalence, one 21700 battery is equivalent to about four AA batteries or two 18650 batteries.

Imalent 21700 battery

18650 vs 21700: Which is Better?

The choice between 18650 and 21700 batteries ultimately depends on your specific needs and preferences. While 18650 batteries are smaller and more compact, 21700 batteries offer a higher capacity and voltage, making them a better choice for heavy-duty flashlights and other high-powered electronic devices.

If you're looking for a flashlight that's easy to carry and compact, a 18650 battery is a good choice. On the other hand, if you need a flashlight with a longer runtime and more power, a 21700 battery might be the better option, as the world's brightest flashlight - Imalent MS18 with up to 100,000 lumens output, runs on 8* 21700 batteries. 

21700 Battery Capacity

One of the key advantages of 21700 batteries is their high capacity, often higher than 18650 batteries. The capacity of a battery is measured in milliampere-hours (mAh) and refers to the amount of energy the battery can store.

While the exact capacity of a 21700 battery can vary depending on the brand, some of the highest-capacity 21700 cells on the market can offer up to 5000mAh of capacity. This means they can provide a lot of power to your flashlight, making it brighter and more long-lasting.

The Imalent SR16 handle flashlight is a great example. It can sustain at 11,000 lumens for 52 minutes and last 98 hours at the lowest 50-lumens mode.

18650 Battery Capacity

18650 batteries also come in various capacities, with some of the highest-capacity cells offering up to 3500mAh capacity. While this is lower than the highest-capacity 21700 batteries, it's still enough to provide a lot of power to your flashlight and allow for a long runtime.

When choosing a 18650 battery for your flashlight, it's essential to consider the capacity, voltage, and discharge rate, as these factors will determine the overall performance and longevity of the battery.

Charging and Discharging 18650 and 21700 Batteries

18650 and 21700 batteries are rechargeable and can be charged and discharged multiple times. When charging your batteries, it's important to use a high-quality charger designed for lithium-ion batteries to avoid overcharging or discharging your batteries beyond their recommended limits.

In general, you should charge your batteries between 80% and 90% of their capacity rather than 100%, as this can help extend their lifespan and reduce the risk of damage.


In summary, choosing the correct battery is crucial for bringing the most out of your flashlight. Whether you opt for a 18650 or 21700 battery, consider factors such as capacity, voltage, runtime, storage, and charging practices.

With the right battery, your flashlight should be a more powerful, reliable source of light that will last for years. 

Imalent 21700 Rechargeable Powerful Torches

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