Learn More About 18650 Lithium-ion Batteries

As far as LED flashlights go, most users will tell you that a light which primarily runs on a 18650 battery is usually the preferred choice. Therefore, I predict this discussion on 18650 Lithium-ion batteries to be quite informative. 

Where Did The Name Come From?

All lithium-ion batteries get their numeric identifiers from their size. In the case of a 18650, (for instance) it’s 18mm in diameter and 65mm long. The zero at the end simply means it’s cylindrical. Some 18650’s will differ in length…but only slightly. The difference is with those that are “protected”.

What’s This “Protection” Stuff About?

This means that a protection circuit has been physically added to the cell. This is preferred since it gives the battery added protection from being accidentally over-charged or over-discharged. If you’re given a choice of protected or unprotected, think of the protected cell as being an insurance policy against possible charging failures. Nominal voltage on a 18650 is 3.7 and shouldn’t be discharged below 3.0 in most cases. The added circuit will make certain that while being discharged in a flashlight, the cell’s voltage doesn’t go below that threshold. On the high end, a freshly charged 18650 Lithium-ion battery will normally peak at 4.2 volts.

What Does mAh mean?

A 18650 battery is a very powerful choice when it comes to operating an LED flashlight. A Lithium-ion’s available power is measured in milliamp hours (mAh). The higher the mAh capacity, the better. This ensures longer lasting power from the battery. Cells are marketed with capacities anywhere from 2100 all the way up to 3400mAh. Do yourself a tremendous favor by reading this article on the dangers of buying 18650 cells that are marketed at capacities ABOVE 3400mAh.

 Pricey Little Devils!

When shopping for a 18650 battery, you may be surprised at the price tag. But what you’re paying for is a very durable and powerful piece of technology. Many of the LED flashlights made today can crank out up to one thousand lumens of light. To drive a flashlight hard enough to produce this level of light, you NEED a powerful battery! And most 18650 lights will only take ONE cell.

Since these batteries are rechargeable, you’ll definitely get your money’s worth from them! Even though prices can easily reach up to $30, it’s worth it. You’re getting a quality made, dependable, long-lasting battery capable of hundreds of charging cycles.

I have many flashlights that operate on 18650 batteries and can tell you from personal experience that it’s a quality combination!

The photo is showing two different brands of 18650… EagleTac and Olight. As you can Lithium-ion batteriesprobably make out, the top one is 3.7 volts and the bottom battery is 3.6 volts. Operationally, there’s no difference between the two.

Please note that they’re often available in both button-top and flat-top versions. Protection circuits are included on both.

The different "tops" of lithium batteries

Flat-top cell on left; Button-top on right

Flat or Button Top?

In many situations, buying a button-top vs. a flat-top makes no difference. BUT, for some flashlights, depending on whether the battery tube features a spring, or a direct electronic connection to the head, it might be a tight fit. This is often due to the added protection circuit, not so much the style of battery. In other cases, the light in question might not work with a flat-top cell. I own a couple that won’t. Although this might be more of an exception, it’s often hit or miss when attempting to marry batteries and lights, and not finding out until the last second if they’re actually compatible!

Bottom line, when shopping for an LED light, pay close attention to the battery configurations recommended for that particular flashlight. Choosing one which accepts a 18650 Lithium battery will ensure many years of dependable service!

Looking to Buy?

It can be tricky shopping for 18650’s, and deciphering the GOOD ones from the BAD!

Therefore I’m suggesting you follow THIS LINK which will take you to an 18650 battery page at Banggood.com. There are many VERY GOOD QUALITY cells at that page!! It’s much SAFER than buying them from Amazon!


What’s your opinion of this article?

Do you have additional questions, or perhaps some personal experience with lithium-ion that you’d like to share?

Please let me know in the comments 🙂



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  1. Thanks for the website. Needed good basic info on the 18650, and every question I had was answered by your well-written and very interesting article.

  2. this post answered my not knowing what protected means, difference button vs flat.

    • Hi Jay,

      “Protected” batteries have a “protection circuit”. This can happen with BOTH button-tops and flat-tops! Therefore flat doesn’t always mean unprotected. Generally, when they ARE unprotected, they’re an “IMR” battery.

      Thanks for the comment.

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