I’d just add that after you do your power budget, if you find you’ll need another battery it’s generally best to combine it all as one bank, rather than a “dedicated” battery for the AP. Lead acid batteries tend to give more amp hours when discharged slowly than all at once. If you’re spending a day at anchor without using the AP a “dedicated” battery will be just excess lead, and trying to switch between batteries is not as efficient as having them all together. If you combine them into one bank you have more flexibility to use them a little at a time with individual loads or with all loads at once without a big loss of efficiency.