My service battery charging system came on had alternator and battery checked OK

my battery checked out after being charged, i brought my alternator in with a fuly charged battery and the alternator was not charging the battery, my next question is how do I know if my alternator is a 170 amp or 150 amp. It is a 2012 Impala LTZ with 3.6L flex engine

Amperage info is in the numbers stamped on the alternator. If that's not legible, call GM dealer parts dept with VIN for ALL the info you'll ever need!