BMW Repair: 1998 528i wont start, resistor pack, blower fan

Question
I have a 1998 528i that wont start, I bought a battery but it still doesn't start. A mechanic needed to jump start the car with another battery passing charge to the front side of the car. He also tried hooking a jumper to the battery in the back, but that didn't work. Once the car started I drove it back home and the next day I had the same problem, the battery that was new is dead and needs to be charged again before the car is jumpstarted with another battery or jumper. The mechaniinc is recomending that the battery needs to be bought at the dealer in order for it to supply the suficient charge that the car needs. What could I do?

Answer
Luis, you have a component in your car that is draining the battery. You need to do a closed circuit current draw test to see how many Amps the car is drawing when not in use (asleep). Your car should draw no more than 40milliamps after the gear selector LED goes out (car's modules enter sleep mode). Realistically your car should read around 20mA for a normal reading. You need a fully charged battery to perform this test. So charge yours up if it will still hold a charge. If your mechanic is unfamiliar with this test then take the car to the dealer. Most often the cause of this is a faulty Final stage resistor pack for the interior a/c blower fan. It is easy to replace and it can cause the fan to come on by itself and over draw current, killing your battery. All of the original steel ones fail due to internal heat damage. The redesigned ones are made of aluminum to dissipate heat faster. If you buy one they are simple to replace. Just look up other posts on E39 Final stage resistor replacement and give me a response to this post to let me know if this fixes your issue.
-Evan