dodge interpret 2004 car problems

I have a 2004 Dodge Intrepid and got my alternator belt replaced about a month ago. I also had the battery and alternator checked and they were fine. Today, the car battery light came on while driving and the headlights were flickering while having the AC on. I turn the AC off and the headlights stop flickering but the battery light remains on. If the battery and alternator were checked in good conditions, is the problem with the belt or possibly the installation?

Yes. Is the belt tensioned properly? Could be too loose.