Originally Posted by Missionpeak BMW
Have a 2001 530i sport/premium/manual- runs great- however I've notice I have to jump/charge the battery when I don't start the car after 4 or 5 days. Battery is 2 years old. No other start issues. Any thoughts would be appreciated.
It's your FSR (Final Stage Resistor) Pack located under the dash. A bad FSR causes your heater fan to slowly cycle on and off at low speeds when the car is off leading to a dead battery in a few days. BMW redesigned this part some time ago. This is a common problem for the E39. Replace it and your problem will be solved.