Car stops after jump start

[mikebalentine]

My V6 mustang had what seemed to be a dead battery now I think it may be the battery as well as the alternator. I had to jump it off, shortly after disconnecting from the other car my mustang would stay running. The lights seemed to deem and then it would just stop. I pulled a battery from another car to see if I could get it to run long enough to get it home. It did. I tried to charge the old battery but the charger said it was bad and would not charge it.
My questions are.
1. In the past regardless how dead a battery was I was able to keep the car running. I have even disconnected the battery and the car would stay running. (I have not tried to disconnect it in the mustang yet)
2. Is there a way to test the alternator without taking it out of the car?
3. The alternator looks pretty easy to replace. The single belt design concerns me a little are there any tricks to replace it if it comes to that?

 

[ChingonStang]

That's usually the "jerry-rigged" version of testing the alternator by starting the car and disconnecting the battery. If the car remains on, then you know your alternator is working fine. If it dies soo after, then you know its the alternator. But your alternator may be failing and may be fluctuating on the amount of power its producing. You can hook up a device that can read how much power the alternator is producing and if I am not mistaken, Autozone can test this with the Alt in your car. If I was you..I would just install a hefty new battery and alternator and be done with it. Good luck.