1999 Chevy Lumina iM lost

I was driving my car when it just died I waited a little bit then it cranked it and boom it starts went down the hill and boom it died charged it up and it ran went acouple of blocks and then it died again then I let it charge while a buddy of mine was passing cables security light has been on for a while and then the volts light came on it has happend before christmas time im pretty sure its the alternator but I just wanna make sure