Replace Care Battery Every Winter

Hey guy, for 3 winters now I have to buy a new battery every year since I park on the street and cannot plug in my car. If it gets REALLY cold the battery dies. The strange part is after I boost my car, I drive it for more than 30 minutes on the highway and it still doesn't start the next day. If I go spend 100 on a new battery, everything will be fine but it seems strange that I have to buy a new battery every year? Could it be the alternator or some other reason? Even in the summer, when I put the key in and start my car, it sometimes makes a slight grinding noise when I turn the key. Thanks!