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e39 dead battery every 2 weeks!!! im lost

6K views 23 replies 10 participants last post by  gemnilvr 
#1 ·
i have a e39 530. i have bought 2 brand new batteries due to the fact that my battery kept dying. i didnt know if the first one was defective so i bough another one. At this point it stays charged for about 2 weeks then it is completely dead. I am able to jump it and then it lasts for about 2 weeks and does the same thing. Right when it is about to happen (maybe a day or so in advance) the windows will start slowing down and the pixels on the radio will start to go missing.

i have previously had my alternator tested and was told that it was fine. i dont know how true that is at this point..

anyone have anything similar issues or advice?

thanks in advance
 
#4 ·
what aftermarket accessories have you put on the car? i.e. aftermarket amplifier are notorious causes for battery drain.

when ur windows begin to slow and you shutdown engine, do you hear any abnormal noises? humming? clicking? or maybe some odd light/trunk light staying lit?

re: alternator - with engine at idle, measure voltage at the battery with a voltmeter. it should read 13.5 or better. If less than that, consider changing the alternator.

let us know ;-)
 
#10 ·
Is the car sitting for two weeks without being driven?
If so, there could be a short somewhere drawing it down.
The way to check it out is pull out ALL of your fuses from the fuse boxes.
Disconnect the positive lead on your battery and then attach a multimeter across the positive post and the positive cable clamp. Set the multimeter for 250mA and then start putting the fuses back in one by one. Eventually you should see some current flowing because the clock and computer will draw a little (50 - 100mA). If you see something spike way above that, then you have found the culprit. Do this with doors shut, trunk lid shut, etc because you don't want the interior lights to come on while you are doing this - the lights will draw a significant amount of power and will show up on the multimeter. I mistakingly did that and it blew that .5A fuse in my multimeter.

But - Like Witeshark mentioned - check the voltage regulator (might be internal to the alternator) - a bad regulator can draw down your battery as well. When you had the alternator tested - did they do it in the car or did you pull it out and have tested in the store?
 
#11 ·
CSI, You need a ESI (Electrical System Investigator). Do you have the V8 with AT?

Some good posts above, but you might need to go to an auto electrical shop (cost might be better than the BMW shop) and have them check it out. Most likely one of the about posts is the answer, but you might not know without the pro check. T
 
#16 ·
The 6/MT is a good thing on a E39 higher mi. 530. I like to start by checking the big ticket items (worried about the AT/V8) and move to the little things when I can't find the problem. Not sure that's right, but it's how I do it. I will see if my little brother has an idea (he's the Mech.).
 
#20 ·
besides the alternator.. what else should be replaced while in there.. serp belt? tensioner?

i called bmw and i guess there are 2 diff types of tensioners. is this easy to tell just by looking. i want to make sure i order the correct parts. thanks guys
 
#22 ·
My bad in a previous message on this thread. I said to attach a multi-meter between the positive post and clamp. I meant to say negative post and clamp.
The Bentley Manual states how to do this test. I've tested mine using the instructions in the manual, but when I posted my previous message my brain got mixed up on polarity and I typed it wrong. Sorry
 
#24 ·
hello, did you ever figure the problem out? mine has been doing this same thing off and on for the past few years and is now starting more frequently. i have found the problems and have done it myself but now i think i may need to replace the final stage unit again and get the wire assembly replaced in the trunk. does anyone know how long the final stage unit should last before replacing it again? thanks!
 
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