electrical problem...alternator maybe? MKIV 2.0

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I have a 2000 Golf with the 2.0 engine with about 105k miles. About 5 days ago, when I tried to start my car it seemed to half crank, and then wouldnt start. I ended up jumping the car, and it started up fine. I thought I just left an interior light on or something, although I don't recall turning anything off. Regardless, it was fine for a bit, and then yesterday same thing, except this time it just didn't start. Here's the really messed up part, I got a neighbor of mine to help me jump it again...I handed him his end of the cables. yada yada...everything got connected up. After 2 failed attempts to start, I realize that he has his side reversed. And I see smoke coming from my battery. I quickly disconnect, and give up trying to jump, assuming the battery is done for, that and Im kind of scared to try jumping it. I went and got a new battery, and replaced it, and now it starts right up. Surprise surprise. The original battery was maybe 18 months old, so I doubt the battery was dead. Maybe Im just unlucky, or is something wrong? It seems like it could be an alternator, although I'm skeptical because, it was fine for like 5 days of at least driving it once a day. Is there any way to test the alternator. Any comments would be greatly appreciated.

Thanks

Jon

does your starter make any growling type noises right after the car starts?

no...theres nothing I can hear that is abnormal, and nothing really ive noticed abnormal aside from the car not starting at the two times i mentioned...which bothers me because i am afraid it will sneak up on me again like a silent fart. hah