e39 dead battery every 2 weeks!!! im lost

[csi9900]

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

[witeshark]

I really suspect the alternator. A look at the voltage regulator couldn't hurt.

[Kai]

Listen to WS, that is almost surly the culprit. Get someone to check it, it is probably putting a slow drain on the battery. If you can't get it fixed then unhook the battery after you are done driving it until you can get it repaired.

[darkhorse737]

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 ;-)

[csi9900]

nothing aftermarket at all. completely stock car. good leads so far ill look into it and see what i can come up with.. thanks for the help so far

[Kai]

With nothing like that get that alternator checked out, good luck!

[Graham Hardy]

Originally Posted by Kasei

With nothing like that get that alternator checked out, good luck!

Try the glovebox light. Mine stayed on even when closed. Two weeks will flatten the battery

[csi9900]

how did you go about checking that out.. i cant seem to be able to tell if its staying on or not

[rashid]

If you look carefully in the full dark, you may be able to make out

[DonJ]

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?

[TIMECRUISER]

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

[csi9900]

no the car does not sit i drive it daily.. its just all the sudden when it stops working.. when i had the alternator tested it was right after i jumped the car after it wasnt starting. so it was in the vehicle at the time of testing..

[TIMECRUISER]

.........how many miles on your E39? V8/AT?

[csi9900]

e39 6cyl 5pd

[csi9900]

112500 for milage