Alternator and big stereo help and curiosity...

I'm currently running four Deka 31 series batteries. I just got my hands on about 100' of 1/0 gauge Knukonceptz OFC wire which I'm gonna use to run to my two Zapco 750.2 amps that are running two WS Pro 485's and also to a Rockford T1500 powering two 12" Rockford subs. I plan on having a lot of wire left over and was wondering if it would benefit my charging system to run that big of a wire off my alternator and to also replace the 4 gauge wire connecting each battery together with the 1/0 gauge wire? My biggest concern is the wires off the alternator. Would I just replace the stock wiring off the alternator with the 1/0 gauge or should I run it additionally to the stock wiring? If I simply replace the stock wiring, do I need to add a fuse anywhere? Is there any possibility of harming anything electronic like the ECM or anything by adding the bigger wire? Thanks for any info.

If you are currently running the batteries and there is no issue, what are you hoping to accomplish? Would there be less loss across the larger gauge wire, yes...but over the length you are talking about its nothing...if you are upgrading your alternator at the same time as the other stuff I could see doing something then. But I'll defer to the experts as I generally don't know what I'm talking about : )

Most boats have somewhere between a 50 and a 100 amp alternator and the charging wire is relatively short. Even with a 150 amp alternator and a 4' run the biggest wire you'd need would be 8 gauge. You can't draw more than the alternator's rated capacity accross it's charging lead so 0 gauge would be extreme overkill. It obviously wouldn't hurt anything though.

I'd probably upgrade the 4 gauge cables between the batteries first as you can draw high current from those.

There's typically no fuse between the alternator and battery. Sometimes it looks like there is a breaker because often the charging lead from the alternator goes to the battery side of the accessory breaker (but not through the accessory breaker). You can just make a jumper to go from the charging post on your alternator to the +12 volt post on your starter solenoid. The heavy gauge lead to your starter will then carry the current back to the batteries. I'd just leave the stock charging wire in place and run a supplemental 10 gauge or better wire.

Also, if your alternator is stock then the factory wire is likely sufficient to carry the full rated amperage of the alternator. Unless you upgrade your alternator it's probably not worth fooling with. I upgraded mine from a 51 amp to a 110 amp and added an extra 10 gauge conductor since the original one was about a 14-16 gauge.