MikeH,
Welcome to the wonderful world of LEDs for bikes /ubbthreads/images/graemlins/banghead.gif /ubbthreads/images/graemlins/buttrock.gif That is why I got into this mess in the first place so I feel your pain. OK, you never did say how bright you want the light or how much you want to spend (I know, $10 to bounce light off the moon) The 18V battery actually kicks up to probably, 21V so you will have to run either 1.25 watt Luxeon Stars (LS) in series or 5 watt Luxeon Stars in series. The 1.25 watters are 3.4V and the 5 watters are 6.8V. This would require six 1.25 watt or 3 five watt LS to tame that battery! /ubbthreads/images/graemlins/mecry.gif /ubbthreads/images/graemlins/jpshakehead.gif
Sure would be bright though! I would suggest (if you do this) to put the six LS's in and add a ton of resistance before you check the output of the battery (should be 350mA is you want stock drive level, or 500mA or so if you want to overdrive the LEDs)
A much cheaper and easier way to do this (~$125)order the Blaster VI from Elektrolumens (tell Wayne to resistor it for NiMH batteries) A 2D light that is light and rechargeable and mount it to your frame. Good luck!
