Removed and cleaned the battery leads on each battery, went from a dark brown/greeninsh to bright copper!
Also cleaned the post and bottom to a nice clean, what I assume is lead.
Haven't tested it yet, but at least I tried.
Also going to improve my dual amp wiring setup at the battery side, it works well, but it's not really up to my standards. Did it almost 7 years ago at this point. Parts are in the mail! Amazon FTW.