Do you have a clamp meter you can test your current set of batteries with? For your battery, if you can measure amps during a larger load, and you see a difference, then cabling could be in order, but if there is no measurable difference then cabling might not be called for. The math probably says it should, but there could be some things that make that link more skewed to show a big difference that does not apply in your case.
The link does give some values for resistance, but the difference between 2/0 and 6 AWG would be huge, enough so IMO that at 6 AWG if the differences were huge, they may disappear at 2/0. Also, in my very limited attempts at measuring battery resistance using a cheap Battery Discharge tester, DL-24P, the battery resistance when full is quite a bit lower when it starts and gradually increased to many times what it was when started versus empty.
That would skew the numbers in the link by quite a bit.
I did some playing around with another link in my signature block this weekend, Mixing and Matching Solar Panels. When Panels in different parallel string have different voltages, the total of all strings is supposed to take the lowest voltage. To my surprise, with 35 VDC, 42 VDC, and 66 VDC for each string I was expecting the voltage once combined to be 35 volts, but the total voltage was 55 volts. Also, the math said I should be losing power by a lot, but the total wattage was nearly the sum of the three panels.
Sometimes there’s things that make the math not add up like it should, perhaps for my solar panels it was an MPPT controller In the mix, or could be somethign else altogether.
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I think what you’re doing is pretty exciting and I would love to move into the RV, but my wife won’t agree to that. Enjoy!!