Here's my contribution:

I replaced my server's UPS batteries every year. This year I saved the batteries for use on the bike. They are 9ah 12V. (I think they are 9ah) I am using one of them with a 55W halogen driving light and a tail/stop signal light wired to the brighter stop lamp. The battery and automatic charger are located in the "cooler" on the back rack. I'm getting around 30 minutes run time before I get a hint of dimming. I'm going to make some changes to get longer run time. My commute is only 6 miles one way so the 30 minute run time works fine for that, but if I have to run errands after work, then I may be pushing against the run time before I can make it home.