Originally Posted by Herk7769
Sure, any resistance will drop voltage and it really doesn't matter where it is as long as it is in the circuit. Resistance is resistance.
Now, hopefully I didn't make a math mistake here, but the numbers feel right. Let's say that your load (power panel, hydraulic jacks, inverter) is 6 feet from the batteries. If you use #4 cable, that will be 12 feet of #4 at 0.0002530 ohms per foot. (Actually these cables have such low resistance it is quoted in ohms per 1000 feet! At 100 amps, that will drop the voltage (let's say it is 12.7 volts unloaded) 303 millivolts or about 2.39%. Decent drop, but most people calculate less than 3% for critical loads and practically speaking, a hydraulic pump is not a critical load. But no matter! If you add 12 inches of #4 between two 6 volt batteries, rather than using a single 12 volt battery, that cable will simply add its own 25 millivolts of voltage drop at 100 amps...which is an additional .14%, for a total drop of 2.53%. It's really like moving the load another 6 inches away from the batteries.
Now, it you go absolutely crazy and use a #0000 cable between the two batteries rather than the #4, it will add its own 5 millivolts of drop, saving you about 20 millivolts (.04%) when compared to the #4 cable, and .1% in voltage drop. Not a number to go crazy about and remember, 100 amps is not exactly a light load!
These are all for stranded conductors.
Your example diagrams have very significant resistances in them, 1 foot of #0000 cable has a resistance of 0.00005 ohms, while 1 foot of #4 has a resistance of 0.000253 ohms, both of which are really small numbers. Sure #0000 has a resistance of around 20% of #4, but it still is negligible when compared to the rest of the wiring, connectors, switches, solenoids, etc.
Bottom line is that it doesn't matter where the resistance is...as long as it is somewhere in the circuit between the battery and the load (or even between two batteries and the load.
I am still mad af Forest River for putting my converter in the rear power bay and running 22 feet of #6 to the batteries up front. That is 44 feet of #6 and costs me a significant amount of voltage drop with a 70 amp converter. At the very least they could have grounded the converter negative to the chassis and cut the effective amount of #6 to maybe 22 feet since the chassis acts like a pretty big conductor, virtually eliminating half of the run and voltage drop!