I have a '91 Baja 290 sport with twin 454s. Has 2 batteries, 2 perko switches.
Was wanting to add on another battery for the stereo system and such and be able to charge off my alternators like the other two batteries. Can this be done? Can anyone share a drawing for this?
Also since I have owned the boat, this dual battery, dual switch set up has not allowed me to say use the starboard battery to start port engine. Thought that was the reason for the perko switches? Buddy of mine has exact boat only one year newer and his is the same. Can someone help?
Thanks in advance.

I have 3 batteries and 2 switches. This is how I wired mine.

Switch position 1 on both switches goes to a battery for each engine.

Switch position 2 on both switches goes to the Stereo/3rd battery.

This way if you turn both switches to ALL, all 3 batteries are connected. As long as I have 1 charged battery, I can start both engines.

The only thing I do not do is run both switches on 2 when the boat is running. I run a big deep cycle for the stereo and they don't like getting that many chrging amps at once. I turn both switches to 2 when coving out or plaqying the stereo for a long time. That way the stereo will only draw off the 3rd battery.

Your other option is to run a battery isolator.

I beleave I got it. I will try this. You have stock alternators?

Griff varry good idea, Just curious when you are on a long cruise what batterie switch numbers do you like to run them on? I would think one switch on one and the other on too to charge both at the same time or am I wrong? Thank's

I added a third battery for the stereo and just upgraded my battery isolator from a two alt. two battery to a two alt. three battery ( Guest # 2503 ) pretty simple addition

Great info guys. I really appreciate it. I have not seen an isolator on the boat. May not even have one on there now.
Just know I have several large primary wires coming in and out from perko's. More than I beleave actually needs to be there. Never had any problems starting so never fooled with.
Thanks alot.

Yes, stock alternators.

Yes, thats pretty much what I do. One switch on #1 and the other on ALL. It make no difference which switch is 1 and which is on ALL. I just vary them and charge the stereo battery as needed.

You wouldn't have an isolator now. It would be something you add between a main battery and the stereo battery. It allows the stereo battery to charge, but won't allow the stereo to pull power from the main battery.

I understand. Thanks. I want to try this and get the ability to start either engine with either battery.
I am going to upgrade the stereo system and want to insure I have enough power to supply.
Thanks again.