S-Chassis.com - Huge Problem Guys Please Help

Well here it goes. i was sdriving to my girlfriends houseabout 30 minutes by highway from my house... and i noticed for a day or two that my check battery light was on..... i have an amp two subs and an after market head unit in my car so naturally i thought that the alternator couldnt handle all the wattage so it was eating some battery power.... i unwired my whole system and the light was still on..... it started with no problem thsi morning..... then all of a sudden on the road the car starts boggin baddddd like it has no energey at all and the speedo and tach are goin nuts blinkers are dimm as ****ttt..... and every time i hit the break the car wants to die more....probably becauseee of the break lights....... ok naturally now i think i have a blown alternator becauseeee IF IT were the batt it really woulndt have made a difference while i was movingg....... the car was jerking way too much and sounded liek i was in 5th gear goin 5 miles an hourr i was about `10 mins away from her house.... i pulled over and got a jump i thought thsi would helppp...no go..2 mins lata same thing. her father came with another batt got it home and tested the alt..... it was holding a decent charge and we charged the battery that was dead.....stilll the battery light is on what the hell could this beee please help i have no car and im a long way from homeeeeeeeeeeee hahahahha jusss kidddin but please help