Postby Hook » April 7th, 2012, 5:29 pm
They'll check the charging voltage with the a/c and headlights on like any other battery. An acceptable level is around 14V, so if you're not getting that, something's wrong.
A charging system is only as good as its weakest link, so before you jump out +$400 on a new alternator, assess the condition of your engine bay grounds and battery charge wire.