they are 3.6 volt 16340 Ultrafire batteries and they are longer I guess because they are protected. They fit ok in my Olight and my Sunwayman but not my 4sevens or Eagletec lights. They do fit my Novatac storm but not my Novatac Special Ops which takes two batteries. When I say fit I'm talking...
I'm holding my Mini 123 in my hand right now and it feels solid. No way I can crush it in my hand. If some other manufacturer can build a light that is just as small and light with the same functions for the same price in higher quality they should do it. For now I'll stay with my Mini 123.
I showed the Tekna knife in my recent video with the splashlight and the original Tekna battery still holding a charge since 1987. See: http://www.youtube.com/watch?v=kIgPALHqOlY