I bought 10" 4/0 wires from an e-Bay vendor, with ring terminals already crimped and sealed (heat-shrink with glue). Those go between eight 405 Ah 6V AGM batteries, also from the end batteries to (-) buss bar and two (+) fuses. Due to the undersized battery bank, will only carry full load for about 30 minutes, not your typical off-grid installation.
I used the hydraulic crimper to terminate 2/0 cables connecting four SI-6048 battery inverters (ring terminal at battery, ferrule where the fine-strand wire goes under a screw). The inverters could produce almost 6 kW each continuously, twice that for seconds to start motors so just an IR drop concern and not ampacity/heating.
AC wire is 6 AWG in screw terminals from the Sunny Islands to circuit breakers. Could have fit 4 AWG, which would allow more derating for a higher temperature location, but 6 AWG is sufficient for my application.
Ground wires for AC and DC don't need to be as large as the current carrying conductors, just sufficient to trip the breaker or fuse in case of a short.