u/Galleon_Rast

I have 2 car batteries in my car to increase the time I can use lights, music, ect. while working on the car with it not running. Both batteries are in parallel and it has definitely increased the time of my car functioning in accessory and still being able to start. I would rather add a relay so the second battery is disengaged from the first until trying to start the car, in which they will remain connected for recharging until the car is turned off. Its a Chevy 350 from the 80's. How big of a relay/solenoid would be required to allow the current of a starter to be drawn through? Thank you.