OK so I have a 2001 60th anniversary XJ 2wd with a 4.0ltr I6. The other day i discovered that what i thought to be my alternator went out after taking it to my mechanic he tells me its the computer that controls the alternator or something of that nature sorry cant remember the exact words. It starts and runs as normal except the battery dies...duh. So my question is what specifically is the problem/part "called" and how easy is it to fix and how much does it cost(not including from the dealer which runs around 7-1000 bucks). Im trying now to decide weather its worth reparing or should i go buy a new vehicle....P.S the transmission will soon enough need to be rebuilt/replaced and the heater core needs to be replaced all in all it would cost close to 3-4k to fix all of this stuff in the end....i just wanna squeeze a little more life out of her till im better suted to buy a new vehicle unlike now im gonna put all my assets into a new vehicle(a used vehicle with high miles starts at 3k in my area :/).