Late last year, I put together a 13W HID with an Li-Ion battery that runs it for 7+ hours. I just ordered what I hope to be a switch that works.

First, I learned that the real difference between a $500 off-the-shelf complete system and a $220 DIY is about $25 (retail) in connectors. You can buy a battery and a light cheap. It's connecting them that's a pain, especially with waterproof parts.

That pbrings up the second point, connecting the parts can be a pain. I had to learn to solder (and buy a soldering gun), and my solders still aren't as solid as the off-the-shelf models. I have also made multiple trips to a local electronics store.

Third, as soon as you order something, the price will go down and a better selection will become available. Batteryspace.com (where I got my stuff), now offers a complete light system like I've been building for $250. It's only $200 with a smaller battery. (Edit: See note at end of post)

Fourth, it's better to have two smaller batteries than one big one. If I had to do it again, I'd look at buying the 4Ah pack (instead of the 7.1 Ah waterbottle battery I have), with a spare battery (perhaps this one). That way, I could just plug in the second battery when the first one runs out, and then charge the dead battery when I get home. That would cost $300, but it would never run out on me.

Fifth, fast chargers are worth it. I have a non-fast smart charger, and it can take 16 hours to fully charge the battery.

Sixth, DIY is an investment in future bike equipment. You really do learn stuff by DIY, which can save you money over your decades of riding. My solders may not be as good now, but they're getting better. And if I want to be adventurous, I should be able to connect up rear LED's to my battery. That would give me a $60 Niterider-like rear light for a fraction of the price.

Sixth, I love the light. 13w of HID is as bright as some car headlights. I also like to say, "yeah, I built that."

Correction: I said above that the complete system was just like mine. It isn't. The complete system has a 10w HID. Mine is 13w.