How do i add a deep cycle battery for car audio?

I am wanting to add a deep cycle battery in the trunk of my car for my amplifiers. Now i know if you run wires straight from the front battery to the back in parallel that wound work but that puts more stress on you alternator. I don't want to upgrade alternators and I have heard that there is a way to isolate... show more I am wanting to add a deep cycle battery in the trunk of my car for my amplifiers. Now i know if you run wires straight from the front battery to the back in parallel that wound work but that puts more stress on you alternator. I don't want to upgrade alternators and I have heard that there is a way to isolate the two batteries with relays. Any help would be appreciated.
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