A trickle charge takes several days to bring the battery back and the car runs fine for 4-5 days and then again will not start as the battery is dead. I recharged the battery and the same thing happened. After the 3rd time I took the car into the BMW dealer and they checked the battery and the voltage regulator and said that both were fine. The car worked fine for about another 5 days and then died again. I then had the battery checked at an Autozone store and they also said the battery was good. The BMW service man said that there could be a parasitic drain on the battery causing the problem. I had the car monitored over night and no parasitic drain was found. The battery is around 4 years old and someone told me that even though the indicator says that the battery is fine........that may not be the case. I'd appreciate your comments.
You need to disconnect one side of the battery, put one lead from an ampmeter on the battery post you have disconnected and the other ampmeter lead on the cable you took off the battery. with nothing turned on on the car , all doors closed the reading on the ampmeter should be no higher than 0.17 amp, if it reads a lot hgher go to the fusebox and remove one by one all the permanent supply fuses looking at the reading every time until you find the circuit that is causing the high reading, this will be the drain. alot of the time it can be central locking system playing up, boot light, glove box light not switching off, stereo wired wrong. hope this helps.
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I also have a 2001 BMW 7401 and my battery goes dead every 1-3 days, the battery is only 1 ½ years old and also checks out fine. I had it to the garage about 5 weeks ago and they replaced a fan assembly under my dash. This involved removing the dash board. Well 3 days later the battery was dead again. Back to the garage for the last couple of weeks where they see a drain but it seems to cycle and not drain long enough for them localize it. BTW, my garage to an electrical specialist who also cant’s find the drain.
I plan on taking a shoot at it myself because i'm technical and have the meters to test.
it might be that there is some build up in the bottom of the battery case causing a short in the battery when moving it around you are removing the problem, i would replace the battery and see if the problem persists.
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