Loud squealing under hood, and battery light comes on, alternator/pulley/belt?

What is your question?

My sons car is squealing, not much at first but the more you drive the more it squeals. He also had to replace the battery last weekend and already the battery light is on. In addition a belt is slightly frayed, I'm wondering what it could be. I just don't want to get suckered in to spending a huge amount of money, I only want to fix the problem. How can I determine exactly what it is and possibly fix? Thank you!