BMW Repair: battery discharges, bmw 528i, negative cable

Question
I have a 1999 BMW 528i. I have been having a problem with the battery discharging for over a year. If I let the car sit for more that 3 days, the battery goes dead. I recently put a charger on the battery and charged it to full capacity. I left it in the garage for one week and the battery had drained to a point where the car would not turn over.  I put the charger back on and the charge showed it required a full charge again. The battery is an Interstate and is less than 2 years. Something is clearly causing the battery to drain. What tests can I perform to remedy the problem?  

Answer
Craig, you need to perform a closed circuit current draw test to see how many amps are being drawn when the vehicle is asleep (16 minutes after last vehicle input, shifter LED will turn off). Your draw should be no higher than 40 milliamps. You want it closer to 20 milliamps. Open the glove box and passenger door. Manually close the latch on the passenger door lock actuator. Open the trunk and manually close the trunk lock actuator. Battery MUST be good and fully charged. Connect a digital ampmeter that can read milliamps in series to the battery (between the negative post and the negative cable or between the body ground and the negative cable. Make sure the shifter LED goes out. Take your reading. Most common problems are the A/C final stage blower resistor coming on by itself or the electrical portion of the ignition changing key position on its own. I would replace both of these out of preventative troubleshooting as they WILL both go bad during the life of your car.
-Evan