My car has been sitting for around a month and 2 weeks now. Yesterday, i went to start the car, and it did not start(dead battery). So i jumped it, and it started right up.. I also recently aquired 2 12's for free, and decided i would finally put them in. So i did. They sound nice. So, after starting the car, i would rev it and hold it at 2000 for about a minute on and a minute off, just to help reveive the battery... while doing this i also had the system sorta bumpin. Not too loud thought because of the neighbors. Thats when the battery light came on, and my volt meter began to drop RAPIDLY. So now im stuck with a low batt, and a dead alternator -i would assume the alt. because the batt volts were dropping while the car was started. What is the most common cause, or reason, for an alternator going out? It is basically a spinning rod, so how is it that it can go out? Do the brushes wear out, or short? whats the cause? Could the problem have also been initiated by having my sytem on?