Living in the suburbs of Birmingham, traffic is a particular problem for me and has long ago driven me into the dark. My first lighting system consisted of a 20w MR16 spot in a reworked Malibu light housing and a 5ah AGM. Ride time was about 1 1/2 hours but the 20w wasn't cutting it at my 30mph cruse speed. I changed to a 35w MR16 and it helped but put a strain on the 5ah battery. I just decided on an upgrade to a 7ah battery and an automotive driving light, using a 35w H3 bulb. It was only marginally better than the MR16 so again I upgraded.
This time, I used both the 5ah and the 7ah together and went to a 55w H3 bulb. That hit the sweet spot for me, plenty of light and a beam far enough down the road to stay out of trouble. I tried it the first time, before daylight last Sunday. I ran the 55w headlight and 6w tail light for about 45 minutes and my 9w parking lights for about 20 minutes. After letting the batteries stabilize for a few minutes, I checked them with a volt meter and found them at 12.5 volts. This is still 90% of full charge so I think I could get at least an hour and a half at full light output.