If you’ve ever found yourself pondering the difference between the two most popular flashlight batteries – the 21700 and the 18650 – you’re not alone. We often field questions about this topic, and that’s precisely why we’re delving deep into it today. By the end of this post, you should have a clearer understanding of which battery suits your needs best.

The Basic Difference: Size and Power

At the core, the disparity between the 21700 and the 18650 batteries lies in their size. The 21700 battery is significantly larger, giving it a higher capacity. The typical 18650 battery can hold up to 3500 mAh, while its 21700 counterpart boasts an impressive 5000 mAh. More power naturally translates to longer burning hours, making the 21700 perfect for prolonged usage scenarios, like a night-long traffic duty for a police officer. If using the 18650, you might need to be cautious about brightness levels during long nights, a concern less pronounced with the 21700.

Bigger Size, Greater Power

The 21700 isn’t just about increased capacity. Its larger size offers more scope to enhance both cooling and power attributes of the battery. To give you a perspective, 21700 batteries can reach capacities of 1400 watts, whereas the 18650 caps out at 800 watts. This difference ensures devices powered by 21700 batteries have an edge in terms of power. So, a flashlight using a 21700 will naturally outperform and outlast one powered by an 18650.

Performance Test: Fenix HT18 Hunting Flash

To highlight the differences, we conducted a test using the Fenix HT18 hunting flashlight, which boasts 1500 lumens. This flashlight was chosen due to its compatibility with both battery types using mounts.

With the 21700 Li-ion battery:

• Turbo: 1500 lumens, approx. 1:40 hours
• High: 500 lumens, approx. 4:15 hours
• Medium: 150 lumens, approx. 20:15 hours
• Low: 30 lumens, lasting 61 hours
• Strobe: 1500 lumens

Using the 18650 Li-ion battery:

• Turbo: 1100 lumens, approx. 1:40 hours
• High: 500 lumens, approx. 2:15 hours
• Medium: 150 lumens, approx. 14:10 hours
• Low: 30 lumens, lasting approximately 53 hours
• Strobe: 1100 lumens

Note: The burning time for the highest light setting is estimated when the light is first turned on at that setting. However, after about 2-3 minutes, due to temperature control mechanisms, the light will automatically drop to a lower mode.

The Case for 18650 Batteries

From the above, it may seem like the 21700 battery reigns supreme. While it indeed outperforms in many aspects, the 18650 shouldn’t be discounted. It’s compact, lightweight, and more budget-friendly. The illumination levels achievable with an 18650 are still commendable, and its price point makes it an attractive choice. For general flashlight use, the 18650 proves more than satisfactory.