Ideas needed regarding a huge battery drain

[John the Blind]

Hi Guys,

Any ideas welcome. Z4M runs fine for a month or so and then goes from starting well on one day to having a battery so flat that the car will not even turn over the following morning. Has happened now on 5 occasions.

Last episode was last week. The car had done 1500mile in a month. It started very strongly and did 40 miles before it was parked up last Wednesday evening. Thursday morning it would not even light the dashboard (10 hours later, 70 amp hour battery so 7 amp per hour overnight).

Only clue is that the the telephone (bluetooth) disappears off the menu a couple of days before it goes flat.

BMW are drawing a blank. Drain tests are providing no clues.

Any ideas or experience. Would be interested in any tech ideas of what would run on a Z4M with the keys out of the ignition which would draw 7 amps per hour. We obviously suspect the bluetooth unit but I am surprised it would draw that much.

Appreciated

John

[TheEnd]

It won't be 7A/h that is being drawn, that's more of a theoretical limit, and it will only need to drop to about 11v before your car won't start.

It most likely is the bluetooth module no going into sleep mode that does it.

[John the Blind]

Battery was below 4v when tested in the morning. I agree with the bluetooth unit being problematic. Any idea what it draws?

[PJ S]

Perhaps the battery is starting to show signs of having a duff cell or two - might be worth recharging the battery with a charger that puts it through a good desulphuration cycle.
If that doesn't work, then a new battery is on the cards - in which case, I can thoroughly and highly recommend the Banner battery I installed in my Accord recently - Uni Bull version.

[scott10005]

bluetooth module,have seen a Z4 before with exact same fault,occured twice before we decide to change the module,then never a problem again.Best to try and get the battery changed at the same time,consequential damage.

[John the Blind]

Thanks guys. On the third battery already so we can rule that out.

the bluetooth unit is still my suspicious. Scott, are you within the BMW dealer network?

[scott10005]

I am

[mneame]

Have you got a tracker? A mate had this problem on his e30 m3 after it was fitted. Turns out that the wiring was at fault and had melted together. Was lucky that it never caught on fire apparently.

[John the Blind]

Many thanks Scott. Passed on your comments and they have agreed to change the bluetooth unit. Fingers crossed this will be the end of it. Battery to be changed also.

John

Edited by John the Blind on Thursday 5th March 18:12

[John the Blind]

Matt, thanks also. Tracker was changed at Christmas as they had similar thoughts but proved not to be the answer.