"can you even get 36 hours at 40 lumens on 2 CR batteries ... that would be quite a feat ...."
Princeton Tec VIZZ: 165 lumen LED, regulated circuitry, 110 hours on medium beam, 90 m throw, 3 X AAA alkaline or lithium, 92 g. I'm in the process of field testing it, but so far, so good. The regulated circuitry should ensure pretty much a constant beam until the battery is tapped out. We'll see, but Princeton Tec has a pretty solid reputation, and I've been using their lights for years with very satisfactory results. So, a qualified yes to the question above.