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Four feet at 100 amps, let's say, for easy numbers.
The charts I have only go up to 0 AWG wire size, not 01/ or 0/2. For 0 AWG cable, the resistance is .0001 ohms per foot, and with a 125A load that would still only be a drop of 0.05 volts.
The drop is roughly--roughly--0.01 volts less each time the cable size goes up one, so I'd guess that's about 0.04 volts for 0/1 cable and 0.03 volts for 0/2 cable. A real difference, yes, but offhand it sure looks like something you could totally ignore.
We're talking about a grand difference of 0.02 volts in a 14.4 volt charging system, or roughly one or two tenths of one percent of your charging voltage being lost.
You can lose more than that with just one poorly crimped cable lug at any point in the system.