The issue is the same as a converter over thin long wiring.
Fatter cable from alternator to battery eliminates the stock alternator charging circuit, and also allows the voltage regulator to hold higher voltages for longer.
In my friend's power wagon with 160 amp alternator, I ran ~ 13 feet one way od 2awg to a lifeline gpl-31XT 125AH battery to ALT(+) stud. I used the battery(-) as it was wired with 4awg from the factory.
When depleted to 50% this battery sucked 100+ amps initially from the alternator, at idle. this tapered to 86 amps when the alternator heated up to 220 F.
I used a 500 amp winch connector:
http://www.amazon.com/Superwinch-2236-commercial-terminals-capacity/dp/B000C7LYYM/ref=pd_sbs_263_2?ie=UTF8&refRID=1J8H2NJ0BYB8BASQRABXThe voltage your vehicles regulator allows will play a large part in the 70% + range.
My alternator has no issues delivering 60 amps plus at 800+ engine rpm, but sometimes it decides 13.7 is all that is required and only a fraction of that flows when 13.7 is all that is allowed