williamwright was thinking very hard :
You are forgetting the internal resistance of the battery. The fact is that
the most charge a car will give a flat battery is around 30A, it it drops off
very rapidly. The high alternator output is to support accessories.

Correct! I have taken the trouble to actually measure it and have seen
20 to maybe 30amps delivered by a 130amp alternator, into a near flat
battery. That level of charge current rapidly declines as the flat
battery gains in voltage.