Goldserve once offer them to use with 6v using a resistor to drop voltage but them later pulled the plug. The LDO regulators are rated for 5.5v max. It's not recommended & will probably burn it without a resistor.
Unfortunately, I have this fancy 2 x cr123a body, and I can't stick any rechargeable in it. I have downboy, but 1 level so boring these days. Test: so far on level 7, light is hot but keep running.