1999 Ford Contour Battery light wont stop

I used to have a pretty big stereo in my car, however I didnt actually use the subs that often. My battery light came on one day on the way to work so I pulled over and it sputtered and wanted to die. I took it home and we checked the battery while it was running and watched the charge slowly dropping. I replaced the battery and it didnt fix anything so I knew it was my alternator. I took it to a guy that doesnt have a Professional shop but works on a lot of state vehicles. He replaced the alternator. Its been a little over a half a year now since that happened. I have since removed my stereo completely except the deck itself. However on the way out again today the battery light came back on. The light is duller than the others on my dash and my car isnt sputtering at all yet but the light is on. HELP!