Master shut off switch charging problem

Here’s an update on this project. I put a painless 250 amp cv relay in the alt - batt. Line. I use a Summit kit that has a #6 wire and 200 amp fuse. I ran the wire through the relay and to the terminal between the front and rear batteries. I power the relay with the same ignition wire feed that turns the m s d on and off which is only hot when the key is in the run position. I then ran the ground side of the relay through a Joes four post Shutoff switch.
I put the fuse in the front battery + line and I plan on adding one to the rear + line between the batt and shutoff switch. One of the other members mentioned that in A crash if one of these lines that are still hot after the shutoff is killed shorts out, the fuses will blow. Great forward thinking there, thank you.
Now it shuts off with the switch and I have 14+ volts at both batteries, slightly less at idle. Almost time to go racing!