What size fuses do I need for 7000 watts?

Stock alt 70ish (upgrading later) i have a 55ah front battary to the 525ah rear bank (6 batts total) (skyhigh ofc 1/0 wire) I need to know what size fuses I need in the front and in the back? Also so I don't start a new thread I want to make sure Im hooking this up right.. one run of 1/0 fused from front batt to the rear bank then two runs fused to the amp? I'm using a sound qubed q1 7000 amp

Well... to begin, you're gonna fry your 70A alternator, in pretty short order. Your 7000W amplifier is really going to need about 8300 watts on the input side, at 85% efficiency. 8300W, divided by 14V, nominal, is somewhere in the 600A range.

You need to address your alternator first. No, a cap won't fix anything. No, more batteries won't fix anything. It's a sad fact of life, but you need to always have enough power supply, before you add so much load.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

If it were me: x2 225amp alternators, x2 runs of 1/0 AWG fused at 300A front and back. x2 300 amp fuses for amp feeds. I would not install that amp until you can supply the juice to it. There is no way a 70Amp alt can run the car and charge that kinda load. You are seriously risking damage to your vehicle and or amp with what you stated above.