Aluminum wire has more resistance per foot than the same size copper.
DanB's #4 AL is 0.408 ohms per 1000'.
Copper #4 is 0.2485 ohms per 1000'. #6 copper is 0.3951 ohms per 1000'.
Meaning if #6 copper is perfect, but you want to use AL because it is cheaper, need to increase the AL wire size to #4 AL.
The distance is half the wire run. Uh...?
The amps flow 150' from the mill to the battery and have 150' of losses,
then turn around and flow 150' back to the mill and have Another 150' of losses.
If the distance is 150', the wire loss is 300'. 150' of Pos plus 150' of Neg = 300'
Some specific purpose wire charts (like some solar wiring charts) figure this "out and back" loss, so need to read the text to see if "out and back" is included.
G-