Dear Pro's,

Ive had an audio system installed in my car for over 2 years now with no problems. However this winter just gone, my battery went flat, I assumed it was dead so i just replaced it, but the same thing happened to the new one. My next thought was that it could be a drain... so I had someone check it out and they told me there was no dran when the car is off. So then i thought it could be the alternator.. Im not an expert but I used a voltmetre to check the battery voltage and this did not increase when i turned the car on and revved it, i also checked the input and output amps of the battery when the car was on and this was virtually the same at around 2 amps so I can only assume the battery is not charging.
However i was told that the alternator is definitely charging at its max voltage.
I am confused and need help as to what it could be.
Thanks