Type 18650, 26650, etc. lithium cell size designations.

What are the differences in the markings of cylindrical li-ion battery cells, e.g.:

18650

18500

16340 (aka RCR123)

16650

14500

26650

Protected

Bare

e.t.c

?

Well, the first two digits indicate the width, and the next two digits indicate the length of the battery in mm. For example, for the popular 18650 cell, this means that its width (circumference diameter) is approximately 18 and its length is 65 mm. And what does 0 mean? It does not matter, because this position has always been zero so far, and it only reflects the way of calculating the length from the last three digits in decimal mm, not mm, as in width, i.e. in the case of a 18650 cell, we have: 650/10 = 65mm . It is important, however, whether the markings contain the word Protected , because the cells described in this way are usually 2.5-3mm longer and 0.5-0.6mm wider than those encoded in the markings of all the batteries mentioned above. The reason for this is the soldering of an external protection system to the bottom of the cell. Cells without protection may not have additional markings, or they are called "bare", "unprotected" or "flat top".

Warning to buyers of these cells :

You can easily cut yourself on low-quality cells, of which there are a lot and are often sold second-hand, so it is important to buy proven ones and do not save on it. If we want good cells for a reasonable price, it is worth trying an inexpensive manufacturer on Aliexpress, whose 18650 cells should be of good quality:

Link to this product on AliExpress

And similarly, 26650 cells from the same manufacturer:

Link to CELL 26650 on AliExpress

Can I charge very different types of cells on one charger?

If we want one charger that can handle very different sizes and chemical types of cells, we need a charger like this:

LINK TO THIS CHARGER ON ALIEPRESS

Further reading

More on the sizes of these and other accumulators and batteries can be found here:

https://en.wikipedia.org/wiki/List_of_battery_sizes