Have you checked that your battery is good? When charged up, it should have about 13.5 volts. A shorted cell will give you less voltage, and dropping.
If you know the battery is good, the way I would chase this is to put an ammeter in series with the battery, to see how much draw you have. Start with a high range and decrease. If it shows an amp or two, you probably have a failed device of some sort. If it is quite a bit more, then I would look for a bare wire or pinch.
To locate a bad device, pull every fuse from the fuse box, taking note of which color fuse goes back where. Take a notepad and pen in with you. Check the draw on the ammeter, you should be down to nothing on the meter, if something has failed. Then replace each fuse one at a time, until you find the 'spike' in your current draw. That would tell you which circuit is the guilty party. Depending on what devices are on that circuit, you might have to disconnect each one at a time to get the exact culprit.
There have been reports that the Becker radio that comes stock on the cars has been known to fail this way, but don't get fixated on that. You could have anything from a left-on parking light (the headlight turned one too many notches to the left), to a fried diode in the alternator.
Don't forget to eliminate the 'simple' stuff, first. It can save embarrassment. Like the time I spent a week chasing a 'no start' problem, only to find out that I had the car in Drive.
Good luck,
Scott