First my setup:
2 batteries connected via perko.
1 800w amp
What I have been doing this year is setting the perko to 1 and using that battery for the whole day. Then the next time I go out, I use battery 2.
My dealer recommended that I use the "all" setting when underway and when I am stopped and just listening to tunes with the family that I use setting "1" or "2" so that I have a backup in case a battery is depleted.
What do you guys/gals do?