my infiniti G20 alternator keeps going out and battery dies.

What brand are you buying as the box store barely rebuild their alternators Napa has new alternators available http://partimages.genpt.com/partimages//89088.jpg Bosch brand $204 plus shipping www.napaonline.com But they are two available so make sure you get the right one

I have the same problem where the battery and brake light come on intermittently. I had replaced my battery and alternator as well. Mechanic said that there is an electrical drain coming from somewhere in one of the attached systems. I believe he said that you may be a voltmeter to see which connection is drawing power when the car is off. It's most likely always draining the battery 24/7.

I had the same problem with my g20 and i had the altenator tested and it was fine......try checking the fuselink for the battery it should be on the ride side in between the battery and the fender under the hood the fuselink cost $17 and i had to get it from a dealership but once i replaced it the car was fine