Originally Posted by rydog
Would adding a third battery be too taxing on the stock alternator? Also if the 1 battery would last for a couple hours that would be fine because then I run the boat a little to charge. Would 1 battery solely used for audio last that long with my set up, estimated of course.
More battery Ah, in the form of either a larger battery or multiple batteries, will be additional load on the alternator, I wouldnt worry about it taxing the alternator. Alternators make for poor battery chargers, so they can struggle to recharge even a single dead battery. So the more battery Ah's you have and the deeper you run that battery bank down, will make you more dependent on some sort of shore charging.
Adding a 2nd house battery would basically double the play time. At the same time, it would meet your current play time goals while only running the bank down half of what it was with only a single battery. This is better for the batteries.
As long as the primary cranking is isolated from the house battery, no need to run engine while anchored, unless the house bank runs down to a point that the system starts to shut down. If you do this on a regular basis, then is time to consider more batteries so you dont need to run the engine (think CO fumes) and the system keeps going without interruption.