I have a 40" totron and HID high (50w) and low (35) beams and a 750W JL Marine amp'd stereo with a single battery. I'm planning on adding a second battery and isolator, but to my surprise, I've had no issues with this setup with everything on. While night riding we tend to take a break about every 45-60 minutes for about 15 minutes or so and I'll usually turn off the lights and let it run. I have ridden for about 5-6 consecutive hours at night like this with no issues.
I did just add a winch and I'm a little concerned that I might not have the juice immediately available for the winch during a night ride, so I'll probably add a second battery soon. Depending upon how much I'm loading the amplifier, I'm sure I'm near 650W at full load.