Adding a second battery to 2011 1801cc

I just purchased a 2011 1801cc that has a group 27 starter battery already installed with a Guest 1,2, or Both switch. I would like to add a new deep cycle battery. My biggest question is how to ground the second battery. It appears the current battery negative is grounded to a bus bar inside the console, and that appears to be 6 ga. wire. My question is do you ground the second battery to the bus bar, and if so, what wire do you need? Note: both batteries are going to be in rear storage under jump seats.

Yes ground it to the ground bus or to the other battery Ty the two negative together. 12v are ran in parallel. Positive should be ran to your #2 position on the isolator switch hence if u switch to "all" position that parallel the two 12v batteries together through the positive and u have built the negative already for that by tying the two together.

But by wiring it that way does the single ground going to the bus bar possibly need to be heavier gauge wire since it is now hooked to two batteries?

Well you don't wire it as above..... That pix has the 2nd battery in parallel. What does that mean?

It's 2 batteries, but electrically.....it is 1 Big 12V battery.

The top pix is what you typically see for your application, but You don't see the option for the alt. pickup. The batteries get charged thru the starter cables.




Now with that said..... You really don't have a dedicated House battery...... This is because which ever battery you select 1 or 2 as soon as you select it.
that is now the start battery and all feeds come from it. And this is why electronics's get "Spiked" with these setups.