Hi:
It may even be a good idea to remove the battery terminals, clean both the posts and the terminals, and inspect the grounds.
As far as the alternator, based on your description, it sounds like the problem exists when you are driving. It could be a regulator going bad or something internal in the alternator that is intermittent. How was the alternator tested?
Let me know.
Joe
Thursday, March 28th, 2019 AT 6:10 PM