If both batteries share the load equally (worst case) then the current on the cable between the two is half the total starter draw. If the cable size is the same as the cable feeding the starter then the resistance of the cable between the batteries is insignificant and for all practical purposes the batteries are equally loaded. (How's that for circular logic? )
The alternator charging current is small compared to the starter draw, and if split between the two equally, half of small on the interconnecting cable, and also not significant, IMHO.
The Constitution needs to be re-read, not re-written!
If you can't handle Dr. Seuss, how will you handle real life?
Current oil burners: MB GLK250 BlueTEC, John Deere X758
New ride: MB GLS450 - most stately
Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510