Dave Plowman (News) formulated on Saturday :
So you are guessing it charges a low battery at 140 amps? ;-)

No, there would need to be a rather large difference in voltage between
the alternator and battery, to achieve that and as the battery attains
a charge, its voltage rises quite rapidly.

I would suggest nearer an initial 20amps, which would rapidly fall to
maybe 3 to 6 amps. A flat to full charge time when being driven, can
require 6 to 10 hours of being driven. Which is why it is always best
to put such a battery on a mains charger for 24 hours, if at all
possible.