3 battery system Twin 150 HPDI 2003

[scarab26]

I have a pair of 2003 Yamaha 150 HPDIs I would like to connect to a set of 3 batteries. One battery for each engine and a third "house" battery. Actually the house battery will be 3 deep cycle batteries in parallel.

I've seen discussions on using 2 of those automatic charge relays (ACR) so that each starting battery charges then charges the house battery charges. My problem is that once both engines charge their respective starting batteries, and the ACR circuit connects both "alternators" to the house battery, you now have connected the "alternators" togeter. I thought that was a no-no because it would burn-out the charging system.

1)
Am I wrong here?

2)
Should I be concerned with current limiting the "alternator" since I have such a large house battery bank?

I use the term "alternator" to really mean the Rectifier/Regulator. Maybe the yamaha regulator has more "smarts" than I'm aware of.

3)
Is it still possible to burn-out the rectifier/regulator if the battery is accidentally disconnected?

I have also read somewhere that there is a secondary output from the regulator.

4)
How is that different from the primary regulator output?

5)
Where do I attach my wire for the secondary output? or where is that wire lead?

If for so reason go back to older 2-cycle outboard engines, would I need to re-wire my electrical system?

I'm so confused, any insight would be helpful.

Thanks,
Mike

[boats.net]

That engine has a built in battery isolator allowing you to charge 2 batterys but the engine will only draw current from 1 battery. It gives most of the charge current to the battery with lowest charge until charged then gives equal charge to both batterys. The isolator lead is optional part number 69J-81949-00-00 and only need to connect to one engine if only have one house battery.