Newbie Battery Questions

[Katdaddy]

I got started down this path on another thread and learned just enough to realize that I know nothing! Can somebody give me a primer on batteries 101? I see numbers such as 18650 and 17670 mentioned. I might as well be reading a foreign language. I'm old enough to remember "see Jane run, run Jane run" so you have an idea of how to present this to me.

 

[Vermonter73]

First two digits are the diameter in millimeters. Digits 3 and 4 are the length in millimeters. The last digit is the shape, 0=round.

25.4 mm is one inch.