On the Amazon US page for the Duracell Durabeam Ultra 1000 Lumens, the first question in the section Customer Questions & Answers asks, "Will this work with Eneloop AA rechargeable batteries using "C" cell adapters?"
The customer who answered reports, "I burned out 2 bulbs as soon as I put rechargeable batteries in. I contacted the company and they said rechargeable batteries are NOT to be used, and I let them know that there was nothing on the package nor insert that said not to use rechargeable batteries. They are sending me a new one." Other customers say they also killed their Durabeams by using NiMH.
The manufacturer's statement that rechargeable batteries cannot be used is reminiscent of Maglite.