Originally Posted by ItsJustMe

Sure you can. Two methods: Empirically (hook them up and see if it work) or open it up, reverse engineer the circuit and figure out what range of voltages it can tolerate.

IMO, they lost some credibility when I said that I would put in a voltage regulator to deliver exactly the same voltage from the LiIon pack as from the AA pack, and they still said it would damage the light.

I guess it's built to only accept the NiMH flavored electrons, the ones from LiIon are too bitter.