Battery jumpers and lenghts.

[Sunking]

Minimum size requirement depends on the fuse size feeding the Inverter. A 35 mm2 cable is equal to a USA 2 AWG good for 115 amps. So unless your fuse is larger than 115 amps, no safety issue.

[bcroe]

With cable adequate for the system currents, and no balancing between parallel sections, there is
no need to make the 1.5M heavier. It might be justified if copper losses are excessive. Bruce Roe

[Jemplayer]

I have a question I cannot get definitive clarity on.

In a series bank of batteries ( 8 RE-B trojans / 48V bank) , the battery jumper (i.e. interconnecting cable) are 35mm2 thick and 30cm long, but between battery 4 and 5 the cable needs to be 1.5 meters long. How thick of a cable should this 1.5m piece be to avoid creating and more resistance between battery 4 and 5?

The same 35mm2 or maybe 50mm2 or even 75mm2 ??