? for the pros

will a 18650 bat always fit and power a lite that uses a 26650 bat

and what about lites that use extension tubes ie: a 2x26650 = 2x18650

It will always work. Think about the the 26650 as a thicker 18650, but with less internal impedance and higher capacity.

Here's the way cells are designated (roughly)

The first two numbers are cell diameter, the second two are cell length, both in mm.

  • 18650 = 18mm x 65mm
  • 10440 = 10mm x 44mm
  • 14500 = 14mm x 50mm

By that, you can tell that the 26650 is a larger diameter but the same length.

does this apply to all #ed bats?

As far as I know, that's the case. As I mentioned, this is going to be a rough estimate - protection circuits and differences in cell construction will result in variations in the actual dimensions.

this info is very helpful


You can buy the tubes at dx to make an easier fit if you find them rattle.

18650 to 26650 adaptor sleeves found here.


Wiki list of battery sizes.