i used one of my ApexPro's with a pair of RCR123A's - just once. Why? well,...
it worked fine for a while, then i heard a LOUD "SNAP" (more of a SNAP than a POP, definitely not a BOOM, Ka-boom, or WHAM...) and the light went dead.
replaced the Li-ion's with a pair of primaries (i.e. CR123A's) and the ApexPro continued to work, and appeared bright. can't say if something in the regulator ckt fried though, but the light still works.
didn't try another pair of RCR's/Li-ions in it.