Then it's pretty obvious it's not the fault of the battery. I would take the alternator off and have it checked, and if it is good, I'd hook up a multi-meter and check to see if you are getting a voltage drain when the engine is stopped. If the alternator turns out to be bad, just replace it along with the voltage regulator. (You always replace the VR when you replace the alternator) If that doesn't work, then you have a source of drainage from somewhere else, like a glove box or trunk light left on. Inspect all the wiring for a frayed positive wire that is grounding out.
My suspicion, is that your alternator is shot.
But, it may be something else. Review the article to help find a parasitic drain source. The pulling of each fuse one at a time is most likely your best bet for locating the parasite. http://www.wikihow.com/Find-a-Parasitic-Battery-Drain