The FourSevens webpage list the QSL's voltage range as 2v - 4.2v. So, voltage wise it shouldn't be a problem. However, there's been much written concerning battery length issues so it's hard to know for sure. Seems early version tailcaps very problematic. I'm going to try one of the Foursevens High Drain RCR123A's once the light's in my now waiting hands. Just returned home to an empty mailbox......
~ Cg
~ Cg