Quote Originally Posted by MLA View Post
Are you looking to install a house bank or add a second battery in parallel to an existing battery bank? Sounds like you are installing a house bank with a dual battery switch. If so, its fairly straight forward to wire up the switch and new house battery.

1) Move ALL (*) cables from the existing cranking battery's B+ post, EXCEPT the bilge pump B+, and move it to the switch's "C" post.
2) with new cable, connect cranking battery B+ post to the switch post "1"
3) with a new cable, connect the new house battery's B+ post to switch post "2"
4) with a new cable, connect from the existing cranking battery GND post to the new house battery GND post.

OFF = all loads isolated from the batteries
1 = loads pull from cranking battery 1 and alternator charges battery 1 when engine is running
2 = loads pull from house battery 2 and alternator charges battery 2 when engine is running
Both = both batteries are combined to each other, all loads and alternator

Using an ACR or continuous-duty relay only will work, but I prefer to have a manual switch in a boat. The relay setup will not allow you to use the house battery as a backup cranking if needed.

* ALL loads include the entire audio setup.

Hope this helps.
My only real concern with this unless im not understanding what your doing it connecting the stereo to the rest of the boat.

If you want a duel battery so you have the stereo on 1 battery and the rest of the boat on the house battery, typically the way most people do it.

I had mine connected by,

Battery 1 is house, + to Pole 1 on switch
Battery 2 is stereo + to Pole 2 on switch

Alternator, starter went to Common connect on the switch.

Ground from battery 1 went to boats ground
Gound from battery 2 went to Battery 1 ground

Factory circuit breaker line for master power went to Battery 1 +
Stereo + and - went to battery 2

This allows you to run your stereo and if it kills the battery you still have a start battery
This also allows you to charge eighter the stereo or house battery, dependent on where your switch is selected.
1 house
2 stereo
3 combines both banks as 1 big battery, also allows charging of all batteries

In this configuration when you switch it to Off it only turns the Boat systems completly off.
Technically you could turn the stereo on still but since the stereo runs off the rocker switch there is no power to it.
But if the stereo shorted it would drain that battery still

<disclaimer im pulling from memory 2 summers ago when i had no ACR>

I personally never connect my Stereo system to the house battery or allow anything from the boat side to ground with my stereo bank. This keeps the noise out.