I have 2 Skar EVL 12’s and a Skar RP3500. So of course I need a dual battery setup. I have the stock battery in the front, I have a marine battery in the back, all ground are good. The amp will turn on when connected to one battery, but as soon as I connect the second battery it cuts in and out of protect mode rapidly. The power wire is run like this. Front Batt>300Amp fuse>second battery> 300amp fuse> amp. The grounds are run like this. Amp> chassis ground. Second battery>to same chassis ground.