My trek 1200 which I use for commuting has a set of profile design airstryke tri bars.
I will soon be needing lights. I was thinking that a very clean and light DIY setup would be too install a cree MR16 led light on the leading end of the bars. There is already a convenient mounting through hole there.
For batteries, I was looking at a set of 10 cr123 3V lithium ion batteries on ebay for 10 bucks.I believe these batteries wrapped in a bit of electrical tape will fit snuggly into the ends of the bars. The inner diameter of the bars looks to be slightly larger than a cr123 battery.
The first battery on each side would have an insulated wire soldered to it's + side. This wire would fish through the bar and out a hole near where the light is mounted. I would use a flashlight type plug inserted behind the last battery. This plug would be the - contact which would make contact with the aluminum bars which would serve as ground.
4 of these batteries should fit with ease into each side giving me a parallel set of 12V supplies. I suspect that this will give me enough juice to get through my almost 2 hr round trip commute. My commute is about a 50/50 mix of "see me" and "see" lighting needs, so, I could get by on a cheapo "see me" blinky when needed if battery endurance was a problem.
I would wire a charging plug inplace so there would not be any need to disassemble this setup for charging.