I've got that problem with all the 3 cell lights. 4 cells will run longer but without electronics do start out with pretty bad efficiency. I'd love to know what the integrated efficiency over life is. I don't guess anyone's calculated it yet.
For a long time I just avoided 3 cell lights. The PS3, now epieon, was my first...and now I'm lucky enough to have a Mr. Bulk LGI on its way. I also got a Sharper Image 1-2-4 LED light that uses 3 AAA...because I have another piece of "equipment" that uses 3 AAA but quits at 1.1V or so.
I've said before about a 3D epieon:
"Some specifics...3.15 Vf @ 250mA, 3.6 ohm series R. So my 3D are at about 4.1V, not completely "fresh". 4D Mag w/NiMH 4.5Ah D cells yields 450mA, and the LED leads get warmer than I'd like, rest of the slug just warm. So, similar to the last one electrically. The cool thing is that 4 NiMH (1.6Ah, RadioShack) AA cells in the Our Best Aluminum run at 410-420mA, and the heatsinking with that light is if anything better than the 3D mag. Still, dunno if I want to run it more than for current measurements above the 350mA "absolute max". The stock single 5mm bulb sure runs above its max, though...80mA! With fresh alkalines...well, I don't think I'll ever put those in the Our Best. Works a charm with alks at 1V, though and should handle a 850mA (HPR52?) halogen if I get bored with it. The plastics don't look heat resistant, but there's enough of an aluminum chunk nearest the bulb that I don't think the plastics would get too hot."
And also:
"Well I just heard back today that a 3-cell one should be on the way along with one of the last "our best..."s so I'm looking forward to that. The 3 cell is probably more efficient and longer lasting than the EverLed, but I'd like one of those as well and have been wishing LEDcorp or someone would do it.
Odd #s of cells suck since they're sold in even numbers, and a regulator, even a partial one, would help with my unreg'd lights running forever but being very dim because I can't get myself to toss batts that still light it up. e.g., Turtlelight. BTW, that 2 led bulb works great in a Tec40!
Only good thing to say about 3 D cells is that it is a nice size...though 2 is nicer if you don't need the extra power, like you really do for a Inretech Trilight (would need 1.7A thru ideal reg off 2 cells...kinda needs 4 cells ~800mA.) but don't for a single luxeon.
BTW, check
http://www.kopin.com/ for news of a new connection scheme that should lower blue LED Vf about 400mV. "