Question about installing a second battery and split charge relays

[boddy 10+ year member]

First of all where can i get a relay that is around 300A i've only saw ones rated for 180A. And are you supposed to run a separate negative wire from your rear battery along your car to the front one, instead of grounding it. I'm going to be running around 220A would everything be alright if i done it in just 1 run of 0 gauge? I know that's more than enough for 220A but if my rear battery goes flat i would like it to charge as quick as it could.

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