For about a week now when I start the car my voltage gauge reads normal, but then after 5 minutes of driving it drops to the lowest on the gauge. So I assume the alternator failed. But if I turn the car off and back on then it will read normal until I start driving again. I thought that maybe the serp belt was loose and the alternator was not getting enough rotation on the pulley, but tightening it did not fix the issue. Any ideas? I am assuming the alternator is going out but I just replaced it 2 years ago. I replaced the battery a month ago.

 

Have you checked all the battery cables and ground cables also the wiring going to the alternator ?

 

Some of those aftermarket alternators are pretty junky - depending on where you bought yours I could definitely see it failing in 2 years. However, like previously noted - check all your basics first just to be certain you're starting from a solid point in troubleshooting.