Lithium Ion 18650 batteries - What are they?

Lithium Ion 18650 batteries have been around for years. Even though the Lithium Ion 18650 style is not “new”, many people are still unfamiliar with them. I will break down what they are, the pros, cons, and if you had the option to purchase an item that uses them, should you?

Why is it called an 18650?

18650 simply refers to it’s size (18mm by 65mm). Similarly, a AA can be referred to as a 14500 (14mm diameter x 50). If you hold an 18650 in your hand, it would look like avery large AA cell.

18650s came about as the need for higher amperage battery powered devices started coming out. Think 20,000 lumen flashlight.

AA batteries just could not produce the amperage output for very long before draining. Let’s compare a typical AA to an 18650.

AA = Rechargeable Nicad or NiMH charge to about 1.4 volts but settle to 1.2 soon after charging. Single use batteries hover at the 1.5 to 1.6 volt range out of the box and are basically depleted at 1 volt.

18650 = 4.2 Volts fully charged that will settle to 3.7. Typical charge current is half of the cells’ capacity (3000mAH battery, 1500mAh charge rate). You would need THREE AA batteries wired in series to equal the voltage of ONE 18650.

Most modern 18650s have a cycle life of from 300 to 500 cycles (charge to dis-charge). When in high-amp or high-drain situations, this can reduce cycle life to as low as 200 cycles. If you regularly exceed the maximum discharge current limit you can decrease the cycle life to as low as 50 cycles. This will occur mostly with NON-PROTECTED cells.

AA compared to an 18650

Protected vs Non-Protected

Protected batteries contain circuitry within each cell that “protects” it from over heating, short-circuiting or over charging and discharging. This added circuitry makes them more expensive than their non protected counterpart.

Unprotected batteries do not have this electronic circuit which allows for higher current capacities but are more susceptible to the above mentioned dangers.

As noted above, protected batteries offer some measure of safety but, you should beware that should you drop or somehow impact the protected cell, the battery can still work but you may inadvertently damage the protective circuit within. Rendering you battery “unprotected”.

Many of todays high lumen flashlights out there that have a TURBO mode will require NON-Protected cells. That extra burst of current draw is what allows the extra lumens.

But use that mode sparingly. It puts high demands on the cell and can cause over heating as well as severely shorten the batteries cycle life. The flashlights WILL work with protected cells but you may not get the full advertised TURBO mode performance.

What To Consider When Purchasing

There are two physical types of 18650s. Button-Top and Flat-Top

Flat-Tops are slightly shorter due to not having the button on the end. In most cases, buying a Button-top vs a Flat-top makes no difference. However, there are many devices that require a Flat-top or vise-versa.

Flashlights are a perfect example. They have either a spring or some protruding connection point that makes contact with the battery. With the battery tube being of a certain length, the addition of the button may cause too much pressure to be asserted against the battery thus causing the button to compress into itself.

If it also happens to be a PROTECTED battery, you may damage the safety circuit as well. The opposite may be true with a flashlight that requires a Button- Top. Without it, insufficient contact can happen and the light will either not work or work but flicker.

Unfortunately, the reality is that most often, the product you buy does not specify Button or Flat. It’s hit or miss. I have some flashlights that I have learned the hard way what type they needed. Either they didn’t work or after some time, I noted the button starting to crush. And with the cost of 18650s, I REALLY wish manufactures were clearer.

Price vs Reliability

As I just touched upon, 18650 batteries are NOT cheap. At least not the good ones. There are comparatively cheap ones out there. But let me just say this… If the name has the word “FIRE” in it, do yourself a favor and don’t buy it. They are cheap for a reason. They are junk. Many sellers buy manufactures “rejects” and repackage them at low prices. Some manufactures are of poor quality as standard practice. I won’t go into who I think is best at this point because that changes all the time but you can check Amazon to compare individual reviews and pricing.

Battery Maintenance

  1. Once fully charged, they keep 80% of their power for up to a year.
  2. Never allow discharge below 3 volts. If you do, re-charge immediately on a slow charge mode. Allowing it to drain below 3 volts degrades the battery faster than a regularly used battery. Many of todays better quality flashlights will give a low battery indication. You should take it seriously. If it indicates to charge, do it.
  3. For long term storage, it is recommended that the cell be discharged to 50% of its capacity (or 3.8V). Place it in an airtight bag or Ziploc and place in the freezer. This should keep the battery conditioned for a long period. When ready to place back in service, remove from freezer and allow to come to room temperature. Then SLOW charge back to full capacity and you are ready to go.
  4. I have used (and still due) cheap-ish chargers. I also have good quality chargers that I feel way more comfortable knowing that they are doing a good job at regulating the charging process. Get a good quality charger. Nowadays, there are plenty of choices available.

Why Should I?

For flashlight aficionados, one thing reigns supreme-LUMES! Todays high power flashlights require 18650s. So they are pretty much the default if you want the power of todays high lumen lights.

In the Search and Rescue world, high lumens, long run times and reliability are a must. 18650s deliver.


Call me one of those “flashlight nuts” that seems to always have a flashlight in every pocket. I have a few that are AA and even some that are AAA. Most of those are still in the packages somewhere. Now, my 18650 lights…are everywhere. The battery maintenance part may seem a bit daunting but I have been using these batteries for years. Some are as old as my original 18650 capable lights and they are still in them now.

The biggest consideration I can recommend is to purchase QUALITY cells from a reputable dealer, along with a good quality voltage regulating charger. I suspect that Lithium Ion 18650 batteries are around to stay and will most definitely only get more popular as capacities continue to increase.

If you have any questions about this topic that I did not cover, please comment below and I will update my post for you and others.

Scroll to Top