Bad alternator?

Another way to check your alternator, is start the car and pull the positive cable off the battery. If the car dies this is a sign of a bad alternator or a bad voltage regulator. I just had this happen to my Dart a few weeks ago.

How does your car run when the lights and all extra electrical things are off? I did this test and the car died so I took it over to the parts store and had them check the alternator, turned out it was OK and my voltage regulator was the culprit.

To answer the second part of your question, I won't put a bigger one in unless you are running a big stereo system or different headlights.