Obviously YMMV and this is just me but I don't mess around with C- or D-Cells if I can help it. Bad enough that some things require a 9v! I have standardized around CR123a, AA & AAA although I'll admit that I've been moving slowly to 18650s where I can. The new breed of uber-weaponlights mostly run on the high powered rechargeables so I'm moving in that direction as much as I can.


IMO most "serious lights" run on either CR123a or 18540 batteries.