fatman caveat.. since it has variable output.. i got really confused when i was driving a single lux 3 at 1000mA from a LiON bat.. but it wouldn't turn down less than 600mA.. well that was the DD current of the particular lux through the fatman.. i had to put two in series to get things to groove.
If you want to be able to dim the lux down (and it's almost silly not to include that functionality).. you might need 3V. LiON does work great if you don't need to dim below 600mA though.. email me for some great fatman tips with LiON.
-awr