I have a 2000 Chevy Venture,when I start it the lights flicker,but only for a few minutes.I was wondering was it the battery or the alternator?
Worn brushes in the alternator will do this.
When the brushes in alternator wear to a point where the copper leads to brushes come in contact with the slip rings, or where the brushes are worn where the brush springs can no longer push the brushes firmly against the slip rings, lights can flicker.
Tester may be right in your case.
In my case (3 years ago) all the lights (headlights included) flickered so fast it was barely noticeable. I have a 2000 Olds Silhouette.
A trip to my tech and a web search pulled up a TSB that showed the alternator may have a wrong sized bolt in it.
He changed the bolt (one from GM) and the flickering stopped for good.