When I go up to high rpms (~3500 and up) my battery light comes on. I'm assuming I just have a bad alternator...Oh, and there is a whining sound coming from the engine compartment but i'm having a hard time pin-pointing the sound.

 

I think you already have. Sounds like the altranator belt slipping, or it's going bad.

 

my friend suggested that it was the tensioner pulley making that noise (bearings wearing out)...don't know if that would cause the alternator to mess up.

 

take you car to autozone they do free testing

 

If the pully on your tensioner is messed up (the whining), it could cause your belt to slip which would be why your alternator isn't charging when you stomp the gas. Sounds like your problem is pretty clear-cut.