Red battery light, needs new alternator? any help appreciated

Hi I have a 06 e90 and driving today I got the red battery symbol on the dash and was still able to make it to my home as i was only about 5 miles away, For a little bit now I was also getting a weird engine noise a really loud whining kind of noise which leads me to think its the alternator or could of been the belt tensioner but with me getting the red battery light today I'm almost certain it's the alternator, anyone who has experience with this who can let me know their opinion, how much this cost them any help is great. The dealership is closed tomm as it's Sunday and I can't find a mechanic open either so Monday I'll take it, also the heat in the car doesn't work properly only until I Take the car up in the 60 mph range it pushes out heat other than that theirs no heat at all the car can be on idle for long and still no heat not sure what could be the problem not sure if it related to the alternator or what, once again any help is appreciated. Thank you