2015 Civic Deep cycle battery Installation
 

So here's the idea. I want to add a deep cycle battery to my civics audio/LED/dashcam system.

I've done this already but it was in a 82 Vanagon Westfalia. It wasn't a hard installation because the batteries fit nicely right under back seat and the solenoid separator was already installed.

My problem here is 2 fold.

1. I want to add the extra battery perhaps in the trunk next to my subwoofer box. I have a nice sized gap between the sub and wall that could potentially fit a optima deep cycle battery. Anyone ever install a deep cycle in a Civic here before? If so, where?

I've seen the starter/deep cycle combos but I don't know if it will fit in my battery compartment or work well for that matter.

2. How do I install a solenoid to separate my starter battery from my deep cycle battery in the Civic? Is there already a diagram somewhere that someone knows about?