RE the OP's Post #1

The advantage of me building my own lights is that when something gets broken, I can fix it myself. Wth the cheap china junk most of it is not repairable.

This is an important point. When my Cygolight HID lamp died, Cygolight wanted $100-$200 (depending on whether they replaced the ballast, the bulb or both) just to fix the lamp. You can by a complete Li-ion system for that at Batteryspace.

Two things I love about bicycle commuting are self-reliance and personal responsibility. If something goes wrong with my DIY, I can probably fix it myself. If I can't, I can buy the part I need for less than what Cygolite would have charged me for a repair.