2001 BMW 325 alternator?

I really don't know what the engine size is or the wheel drive at this moment and I apologize for being unprepared but last week my car stalled and wouldn't turn over. Before that the radio would turn on and off and the battery light would come on but the car engine never died. When the tow truck driver jumped it the battery would not hold the charge for long. The tow truck driver said it's the alternator and it happens often on BMW's and Mercedes. Before I purchase an alternator I wanna make sure I get a second opinion. I replaced the battery about 2 years ago or so. When I went to get a smog it said something about the camshaft.