Mitsubishi Repair: Battery draining when car runs., mitsubishi eclipse gsx, advance auto parts

Question
Anthony,
I have a 1995 mitsubishi eclipse GSX 2.0L Manual tranny.
I have just replaced the starter and alternator and when I jump start the car(because thats the only way I can get it running) it will idle fine for a few minutes and when I place a voltmeter on the battery it starts at 14 and slowly decreases in voltage until it hits about 4 volts and then the car dies. it seemed like the alternator but like I said I just replaced it and double checked for frayed wires and made sure everything was plugged in correctly. I do know that the previous owner had tried to pop start the car and had the pos and neg wires backwards on the battery(dummy).Could this have caused a short somewhere? if so, is there any way to locate a short in the system? where would I look? I checked every fuse and the check engine light is not on.
thank you, James

Answer
James,
When the car was pop started with the battery cables reversed, that may have damaged the battery itself.  Have your battery load tested.  Most major auto parts stores like AutoZone or Advance Auto Parts provide free battery testing.  If your battery is bad, it will severely decrease the life of the alternator.  If the battery is more than 5-7 years old, it's probably time for a new one anyways.
Good luck!