Originally Posted by Zin
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.
Good job Zin. That's a pretty heavy load for the battery and may reduce its longevity. Also be careful not to overdischarge the battery since this will permanently damage it. Here are some (no load) voltages for a 12V lead-acid battery and the approximate corresponding remaining capacity:
12.65V = 100%
12.45 = 75%
12.24 = 50%
12.06 = 25
11.89 = 0%
A 20W headlight would reduce the current draw and would still be very bright. You didn't indicate whether your tail light is tungsten or LED, but either way you could have the tail light on all the time, and connect the stop light filament to a switch on your brake. I did that and the drivers keep their distance.