Pitr, I run a 6V, 3W halogen with a 5Ahr sealed LA battery. On full charge, the battery should run the 3W (draws about 1/2amp/hr) for about 10 hours. In the real world, it probably won't last quite that long.

I left for work this morning at 5am. 1 hour, 10 minutes to work in 49deg weather. Left the light on inside (by my work station) until 2pm. Still bright. I turned it off and plugged it in because I wanted to make sure it was bright enough to get me home.

I don't know for sure how long it will last but at 3W, drawing about 1/2amp/hr, you should get plenty of run time.

Adding an LED rear tail light will draw a little, but I wouldn't think it would be very much.