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.
Metric system (millimeters) is used almost always when we see
li-ion battery with numbers like:
18650
18500
16340
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.
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.