Ya, I would run half the day on 1 battery, then half the day on the other to keep them charged.

I have an onboard battery charger on my current boat. I was thinking I should also carry an extension cord.

I have boats with a single motor and dual motors that have 2 battery set ups. Always ran on All. If I planned on parking some place for hours I may go to one just in case I ran it into the ground I would have the other to back it up but I have never had an issue. Now I have found if you leave your batteries on All when the boat is stored and have a bad one it will suck power out of the good one so I always turn them off when the boat is not in use unless its sitting in water and needs the bilge pump on.

I have a 25' set on every boat. You never know when someone else might need a jump.

Yep, last year I was at put in bay and it was raining the entire weekend. With no access to shore power to keep the charger going, I went ahead and left the batteries all on in parallel to make sure the bilge pumps could run as long as possible if needed. Id rather deal with dead batteries than a sunk boat.

So, some of you don't have hard wired bilge pumps ? Meaning, if you turn your batt switches to off, your pumps get no power ?

No, its hard wired of course but If the switches were off, the bilge pump would drain the one battery that it is hard wired to. This is just a single engine boat that only has one bilge pump (have plans to install a backup). But by having all 3 batteries on and paralleled together, I have 3 times as much battery power to run the pump if needed with the constant rain water.

I have an on board battery charger. I leave the boat plugged in all the time at home. It acts as a tender to the batteries. I don't seem to have battery issues.

How is 2 alternators on a boat different from dual alternators in a diesel truck ?