Yes, I mis-spoke (mis-wrote?)...unlike incandescant bulbs, my understanding is that LED's need a minimum voltage drop to shine at all (band-gaps or something like that). I understood you need a battery voltage well above this voltage (since batteries fade), that pulsing was a common intensity control mechanism, and that current regulation was essential.
I had also heard that the most efficient setup was to use a regulator to keep the voltage from varying much, not sure why, perhaps just to keep intensity constant. Also, the smaller the resistive component in whole setup, including in the current limiting bit, the better, to avoid waste heat.
Do you have any of your circuits posted? I want to modify some of my old headlamps to take LED's...
P.S. Check out the SAFT web site...there are all kinds of Li batteries there (except LiFeS2, the Eveready formulation), not all easily available, with all kinds of energy storage densities, maximum currents, tempature characteristics, etc. I think some of them are superior in terms of joules/kg than the Eveready batteries at low current draw and perhaps at cold temperatures.