At best no more than 25 percent over the idle amperage of current draw of the amps. that is what I was taught. so like say for example, you have an alt that idles at 200, your current draw from all of your amps and factory things like ac or other electronics should not be more than 250 amps. This is a general guideline, assuming that your amps eat up that much power, not taking in to account box rise and other factors.
my setup isn't like that because there is no dual alt bracket, and I don't want to remove my ac just yet to fit a 2nd alt. that is why I loaded up on the batteries, and I should actually have 1 more lifeline batt