Lets's talk multiple battery setups. (3+)

[dusty2221]

Lets discuss running multiple battery setups. More specifically, a 2 Stereo and 1 Crank battery setup.

I've got the basic knowledge, as in, I know in order to wire the secondary stereo battery, you simply connect the + and the - from the primary stereo batt. Then, when the perko is on "2" it will pull equally from both batts, effectively doubling the play time. When the perko is set to "all" with the boat running, all 3 batts would be receiving a charge.

Here is where I am unsure, is it necessary to
A) Buy a higher output alternator
B) Have the factory alternator rebuilt

Beyond that, is there a "benchmark" that you pro audio guys go off of to determine when a 3rd is needed? I haven't completed my install yet, but I built everything to allow for the addition of the third in the event it became necessary. At what point is it just a waste to add? When is it absolutely needed?

For reference, these batts will be powering a 4 amp system (2 for the HLCD towers, 1 for Sub, 1 for Cabins, and more LED lights than a boat should have. What I am wanting to cover, is that I have a system capable of providing a solid 8 hours of music without needing a start. I doubt I would ever have a day at the lake where I sat for the entire day, but it will be nice to have the piece of mind knowing that even for a 4 hour sit, I have no issue whatsoever and could go hours longer. What I am thinking to test the system ability, would be playing the system for about 4 hours non stop and then flipping my led's on and see if I can garnish another 3-4 hours from it, and have it not cut out from no power.

I'm sure I will have more questions after getting some replies, but this should get the convo going. And who knows, this might spark up some more of my MS Paint drawings.