New battery dieing? Alternator Problem? Bad battery?

I have a 2001 Mitsubishi Eclipse GS, on the 2.4L engine.

I recently just replaced my starter and my battery about a month ago. Now I'm having a problem with my battery dying. This problem does not occur often (about once a week), I would drive somewhere, go back to start my car and there is no crank. The battery seems like it's dead. I go out to check the voltage of the battery and it reads 13.0V (car was still hot and its summer). I have one of my friends come and jump my car and wallah! It started.

I've checked for a parasitic draw, my battery is only pulling 0.1 amps while the car is off. So a short is ruled out.

I went to autozone to test the alternator and battery, they said everything was fine. I went to WalMart to have the battery load tested without being inside the car, they said that it was good.

What I found interesting though, was the voltage of the terminals when under full load (headlights, AC, fan, radio, blinkers) on. The voltage drops down to about 12.7V while under full load. When all accessories are off though including radio, the voltage goes back up to 14.5V.

Is it my alternator that is going bad? Or did I receive a bad battery from WalMart?