18650 battery dimensions explained. Wild, wild world of Lithium-ion batteries

What does 18650 mean in batteries?

The Answer:

18 - The first two digits "18" stand for li-ion battery diameter in millimeters. In this case width of the battery is 18mm (millimeters).

65 - The third, and fourth digit stand for length in millimeters. That would be 65mm.

0 ? -  For those who want to know why zero is there, this is how battery manufacturers calculate batt. length: 650 divided by 10 is 65mm.  Since we are simple people we will forget about zero for now.

18mm by 65mm - 18650

Metric system (millimeters) is used almost always when we see li-ion battery with numbers like:

18650
18500
16340

16650

14500

26650

Above are the most common li-ion battery sizes. So, next time when you see 18650 battery you will know for sure meaning of all these numbers.

Let's see what we have learned today.

What is 26650?

26mm - diameter

65mm - length

Battery dimensions in a real world can, and will vary.
Important:
These measurements are for bare Li-ion cells only (also called "unprotected" or "flat top").
If you see "PROTECTED" printed next to 18650, 16340, 14500, 26650 ...  that means that external protection circuit board is welded to the bottom of the bare cell, and flat wire is added to the side of the cell.
Because of added external protection protected Li-ion batteries are 2.5mm to 3mm longer, and can be 0.5mm wider than bare Li-ion cells.
I will explain what Protected Li-ion battery is in one of my next posts.

By the way, 16340 rechargeable li-ion battery is also called RCR123. It is the same size as CR123A primary (non-rechargeable) cell. First letter "R" means rechargeable.
And again, if word "Protected" is printed next to 16340 (or RCR123), battery will be longer than regular CR123A by 2.5mm to 3mm.

14500 Li-ion is the same size as AA battery, but it should never be used as a replacement for regular (Ni-Mh) AA battery. Why? Well, stay tuned I will keep posting some interesting stuff.

Example:
As you can see from this photo battery size will vary slightly. This is one bare unprotected 18650 battery. Flat top.
Protected 18650 (or any 26650, 16340, 16650,14500 ...) lithium-ion batteries will be approximately 2.5-3 mm longer, and 0.5 mm-0.6 mm wider in diameter.

18650 Battery Review-Vape & Flashlight communities need some real battery tests.

18650 battery test-reviews is what I will start doing from the next week.

It will ne very interesting to see how 18650 batteries behave under different working conditions.

These bench tests and reviews will include:

• Visual discharge graph (curve) at various continuous and pulse current loads.

• Battery Amp limit.
• Real capacity (cell will be discharged from full charge to the lowest voltage discharge cutoff limit).
• Working temperatures during discharge in real time.
• Original Battery Specs - datasheet from manufacturers.

You will be able to see the actual performance of the battery cell (in various situations), that you might be using already or that you would like to buy somewhere online but not sure about performance.

Why am I doing this?

Answer: Safety!

It is getting out of control.

Flashlight community is pretty much safe, because 99.9% of today's LED flashlights are running on 18650 Protected batteries.

One, and only independent battery tester is HKJ. You can trust his extensive Li-ion testing 100%.

The lithium-ion safety risk is the highest in vape (electronic cigarette) community that is growing very fast.

Lack of proper li-ion 26650,18650 battery knowledge is the biggest enemy for average vape (ecig) end user (vaper).

To make this already dangerous situation for vaping users even more risky we can see more, and more companies (usually Chinese) releasing unprotected vape 18650, and 26650 batteries with exaggerated Amp limit rating numbers. Sometimes 500% over actual battery Amp rating.

It seems that box mod e-cig batteries are becoming good source of income for individuals who represent themselves as "independent" battery testers.

I will talk more about these "unbiased" battery tests too, and what tricks they use to make battery performance bad, or good.

Just some of the 18650 batteries that will be tested with very accurate (lab calibrated) computer battery analyzer:

LG HG2 

LG HE2 and HE4

LG HD2 and HD2C

LG HB6 

Samsung 30Q , 25R, 20R

Sony VTC4

Sony VTC5, VTC5A

Sony VTC6

Panasonic NCR18650GA, NCR18650B, NCR18650PF, UR18650NSX

Some very good, and some really really bad, and dangerous rewraps will be tested as well.

Many more batteries will be tested and posted on this blog. This is just a beginning...

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What does "18650" printed on Li-ion battery stands for?

Now when you have your new LED flashlight, you start looking for the best li-ion batteries money can buy. Searching the internet will not reveal what 18650 stand for. Everything is so confusing, and all those numbers: 18650, 16340, 18500? Thousands of batteries to buy online- the question is: will they fit my new flashlight?
Is this the right battery for me? Will this type of li-ion battery work in my flashlight at all?...

Do you know what all those numbers actually mean?

I will start with 18650 Li-ion battery. 

Why manufacturers use number 18650? No, these numbers have nothing to do with battery chemistry.

These numbers, printed on li-ion rechargeable battery cells are so easy to forget if you don't know what their meaning is. Numbers, and abbreviations printed on rechargeable li-ion batteries are not that complicated after all. I will explain it in my next post.

Everything about Li-ion battery (well, almost everything)

Very useful info about Li-ion battery cells you can read at battery university web site.