Dave Plowman (News) brought next idea :
I'll bet those charge figures are a peak output plucked from the air.

Makes you wonder how the car alternator can re-charge the battery so
quickly if 6 amps is a safe amount into an 80 amp.hr battery which is
towards the large size for most cars.

Peak of the ac current and only into a large and very flat battery,
output will go down drastically as the battery take a charge and builds
up some voltage.