I use Sanyo 2700mAh cells in mine as it's my edc.
If you use 14500 Li-ion cells, you may have issues with correct fit. I have a pair of trustfire blue protected cells and they are a bit long. I have to untwist the head about 1/10 of a turn for the switch to work properly as these cells are a little bit longer than AA cells. Other 14500 LI-ions may fit better, but these are all I had to try.....
PS - sport69, I see you're in Portage, IN - I'm originally from NW IN. Haven't lived there since college though - GO PURDUE!