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This kind of uses battery size term – so named for its lithium ion at a size of 18 mm diameter, 65 mm and cylindrical shape.

https://en.wikipedia.org/wiki/18650

https://en.wikipedia.org/wiki/1865

https://en.wikipedia.org/wiki/1865_in_the_United_States

https://en.wikipedia.org/wiki/1860_Mount_Lebanon_civil_war

Best 18650 Flashlight of 2018 – Top 9 Flashlights & Buying …

Wow That’s Crazy! 17 Brightest Flashlights 2018 [AAA to 18650]