E46 battery drain ??

what's the probable main cause of a battery drain overnight on a e46, the battery is in good condition firstly and and the alternator seems to be doing its job, after lots of googling the most common issue seems to be the Final stage resistor not going off when you shut off the car so to check that i have removed fuse 50 to elimiante it to see, last time car was driven was tuesday morn and started ok , came out this morn and could not even get an igntition light. really dont know what else to check now

Was the car locked? I left mine unlocked once overnight and it was completely dead the next day, no idea why?!?

FSU would be my first guess but you have eliminated that as you say.

My Dad's old 325Ci used to do this and it was found to be the cigarette lighter

I would remove the final stage resistor altogether. That is the most likely thing. There are multiple fuses that would need to be removed to eliminate this.

Also, do you have any aftermarket equipment in the Carole stereo or alarm that was not factory fitted? That would be next on my hit list.

After that I would disconnect the positive terminal on the battery & put an ammeter (multimeter set to amps) between the battery terminal & then, one by one, remove each individual fuse & check to see if the current draw drops. This will help pinpoint the source of the current draw.

It could be a faulty head unit, a sticking relay or anything.

What about fault codes? Is there any showing? Also, was there any work done on the car recently where something could have been inadvertently/accidently interfered with?

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Originally Posted by JohnH

My Dad's old 325Ci used to do this and it was found to be the cigarette lighter of ecig called Aerotank

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I am still not find out why the battery drain away so quickly.. I think I need to hire an expert now.