what's "18650" stand for?

[40apple40]

anyone know why 18650s are so called?

 

[Quension]

Physical size: 18mm wide by 65mm long, with the trailing 0 supposedly meaning a round cell. (I say supposedly because I've seen round cells named with a 5 there, but whatever.)

Protected batteries might be a bit larger.

 

[Paul_in_Maryland]

By convention, 18 means "at least 18.0mm but less than 19.0mm." In other words, a cell could be 18.9mm wide and still be an 18650 or 18500. That's why FiveMega's 18xxx bodies have an inner diameter of a generous 19.1mm.

18xxx cells by Wolf Eyes, Pila, and certain other brands run longer: about 68mm. The differerence can present fit problems, and connection problems, when mixing brands.

 

[40apple40]

many thanks for the replies.

in future i can now pretend to know what i'm talking about :twothumbs