What you are talking about doing, putting a battery in the trunk, is now totally obsolete. Get a 5 lb, 4" x 5" x 7" lithium battery, mount it up front, or under the car in the inside of the frame rail near the starter. You save 20+ lbs of cable, 50 pounds of battery, reduce complexity, and its cheaper in the long run. Because it lasts 10 years and less wiring cost.

This little Anti Gravity battery spins my 13:1 Hemi over like the plugs are out of it:
https://www.amazon.com/Antigravity-Batteries-Lithium-Motorsports-Battery/dp/B06XKQNJXY