Wiring help for trunk mount battery

^^This is what I started out with, but that run of wire back and front may ADD to the voltage drop/ overcharge problem so many of these girls have. That is why I suggest a big relay or continuous duty solenoid to run the car loads

Another concern by many is surge/ spike on disconnect due to the alternator, say, using a "one wire." There exists load protection devices, primarily for marine multi battery use. I have not researched them. "Load dump" and other names