I have a 1983 300SD TurdoDiesel. I recently let a friend of mine use my it and he accidently left the cd player on and the car died. He jump started it, and now the battery does not seem to hold any power. I charge up the battery, but by mid-day, the car is dead. At times when I'm driving, the electrical systems in the car slowly seize to function, lights, windows, speedometer, everything. If I remove the negative from the battery during the day, the battery seems to stay charged. I'm thinking it's a bad alternator, or could it be something else?