FASing at night?

[NH Titan]

I have a new battery (regular). Should I not be FASing at night? My headlights do dim a bit but still provide plenty of light. Other than the killing my battery are than any other things that I could be damaging?

[PaleMelanesian]

Battery is the main deal. Get some kind of voltage reading and watch it like a hawk. If it gets too low, switch to neutral / engine-on coasting.