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post #1 of 118 Old 8th January 2010, 06:28 PM Thread Starter
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Got Battery Drain Problems? Check Here

My Battery Drain Saga

Hi All,

I thought I’d write this to assist any of you that have battery drain problems on your M5’s, I know I certainly did, and I wanted to get to the bottom of it.


A bit of background, my car is a 2001 Facelift BMW E39 M5, European RHD model, in the UK. Fitted with the comm’s pack with the Motorola V50 cordless phone, the Traffic Master traffic information service, Widescreen Monitor with MK3 Sat Nav Unit, CD changer. No voice controls, no Bluetooth, no sunshades.
Completely electrically stock aside from some LED angel eye rings and LED number plate lights.

Please note that from here on in I’ll be referring to my car, so you need to understand that nearside/passenger side is the left hand side of the car (RHD), and offside/drivers side is the right hand side of the car (RHD). Also for our American friends, the ‘boot’ is the ‘trunk’ and the ‘bonnet’ is the ‘hood’.

I measured voltages in three places throughout this, the Battery terminals in the boot, the jump start posts in the engine bay, and the VB reading on the secret menu of the On Board Computer (OBC- Test No 9). The positive engine jump start post is on the passenger side bank of the engine near the plenum, the negative jump start post is on the driver’s side suspension turret.
The voltages between these three positions is drastically different, bear this in mind when your doing any readings, and try to be consistent where you take your measurements from, temperature has an effect on battery voltage too, a battery is generally considered to be fully charged at 12.65v (disconnected from anything) and 11.89v fully discharged, at 20 degrees Celsius, adjusts being made at -0.022v per degree below 20. I.e. fully charged at 0 degrees Celsius would be 12.65 - (20 x 0.022) = 12.21v generally, rule of thumb, not exact science.


Right, here we go….

Back in October 2009, I came to my car one really cold morning, turned the key, flat battery, I got out my multi meter and tested the battery at the jump start posts in the engine bay, 10.7v. No problem, dead battery, expected in cold weather, went and got another one from a local supplier (Halfords for the UK’ers).
After a while, I was having problems again, posted on M3torque my problems, Kumaran (M5 London on both the M3torque forum and the M5 Board) discovered that the battery I had was not suitable for the M5, too low cranking power and amperes and I needed another. I spoke to Halfords who had no bigger batteries, and managed to negotiate a full refund and I had been incorrectly advised by their staff of which battery was right for my car.
Again, Kumaran came to the rescue and pointed out the perfect battery, practically OEM size, 920CCA and 110AH, the Bosch S5 015, available from Euro Car Parts, product code 444779008.
Fitted the battery, checked the voltages for a few days, and seemed ok, lower than I’d have liked, but put it down to the cold weather. (12.18v at the jump start points).
At this point I’ll mention that I had checked the voltages with the engine running, at idle, it measured 13.5v on the OBC, 13.92v at the jump start posts, and 14.2v at the battery posts, so I knew my alternator was ok, and this showed the variation between the different testing points.

Fast forward 6 weeks later………in the UK we have had a cold snap, temps down to minus seven degrees locally for me, Xmas and New Year means I’m not at work, short journeys, a lot of electric systems in use on the car.
Come to the car one morning, turn the key, click click click, flat battery, jump out and check it, 10.98v at the posts, and its minus 4 degrees outside. Jump start the car and alls well, charging fine. Take it for a run for 10mins and then return and start my series of paranoid voltage checks over the next week…….

I discover that the battery is 12.6v after my 45 min drive to work, and if disconnected from the car, despite the low temps, it will hold this voltage all day. Fitted to the car, its 12.4v and 11.9v by the morning, I obviously have some sort of current slow current drain on the car. The car still starts at 11.9v, and infact does so, all the way down to 11.1v. I remove the battery and have it load tested and it pass’s A-ok.

So I now start reading the internet furiously, to see if anyone else has similar problems, and it would appear it’s a common thing on the aging M5’s, so I decide to investigate it myself.
I learn about the cars ‘sleep’ and ‘awake’ cycles, in which systems in the car are powered down after around 15-20mins and the electrical system goes into idle. So I put the car in sleep mode, and connect an amp meter, to locate the circuits with the current drains.

Sleep Mode

To do this, first of all, you need the car to be some place safe and the weather on your side; you will have the passenger door OPEN (not just unlocked) for most of the day, and the bootlid too.

1) Open your glovebox, remove your torch from its socket, turn the two white clips 90 degrees and lower the front fusebox.

2) The door switch is in the striker on the B-pillar, put the plunger back and then wedge it, I used a wad of paper. Do not close the door now until you’re finished

3) Open the bootlid, and then using the shaft of a screwdriver, click the latch back (So the car thinks the boots shut), the boot light should now extinguish. Do not close the bootlid until your finished.

4) The car is now ready for diagnosis. An amp meter needs to be connected in series with the cars electrical system, not in parallel like a volt meter, so setup your amp meter to read a figure somewhere around 2A max, giving you 3 decimal places to work with.

5) Disconnect the battery negative lead, and somehow connect one of your amp meter probes to it, I inserted mine under the securing nut and nipped it up to grip the probe. Connect the other amp meter probe to the negative post, I used a small g-clamp for this.

6) The car should kick into life, the glovebox light will be on, the nav system will probably be flashing and reading discs, you’ll probably see 500mAh on the amp meter (0.500). This is fine, leave the car for 20 mins and when you come back to it, the glovebox light should be off, it’s in sleep mode.

Circuit Testing

Here’s where the fun starts, and its better with two people, one watching the amp meter, one pulling fuses, you’ll need a pen and paper to note down which fuses effect the amp draw.

Starting at either the glovebox fuse box, or the boot fusebox (behind the trim on the drivers side of the car, in the boot) pull one fuse at a time, note its effect, and replace it, then move to the next one. Sometimes this will ‘spike’ a circuit connected to the sleep systems and ‘wake up’ the car, can’t be helped I’m afraid, wait another 20 mins to re-enter sleep and continue. Also be careful not to nudge the switch for the glove box door, this will wake the car from sleep mode too.

UK Glovebox Fuse Layout

UK Boot Fusebox Location

UK Boot Fusebox Layout


On my car, it was drawing 68mAh (0.068) in sleep, which I believe it too high. The only fuses which effected the reading are-
Fuse 57 - Telephone - Dropped it 58mAh
Fuse 56 – Nav System/On Board Monitor – Dropped it 13mAh

I also, heard that the Trafficmaster system has a parasitic drain on the system, and is permanently supplied. When the traffic master unit is unplugged, the draw dropped by a further 3mAh. Not much, but as it’s now redundant, and it’s easy to remove, I’ll remove it anyway.

So, the problem in my case certainly looks like the phone, i checked the phones display and its was powered up, with “Charging complete” on the display, I quickly un-plugged the phone and then reconnected it, and the amperage dropped to 10mAh (0.010), with that and the traffic master unplugged I got it down to 8mAh (0.008) and 60mAh drop, and I suspect I have found my problem. After disconnecting/reconnecting the phone, the handset remained in a powered off state.

Follow Up and Notes

Don’t forget to remove your paper wad, and you press the button on the bootlid to release the latch before you close it.

So the next day, I repeated the test, phone fitted, and then phone disconnected and see if the results are the same, they were, so that phone was the fault, and removing the phone handset from the car cancelled the drain, and satisfied me that my problem was solved. It dropped from exactly 68mAh to 10mAh again, and the traffic master disconnect dropped it to 8mAh again, a perfectly repeatable test J
So I, removed the traffic master too, every little helps!

I know a 60mAh current drain on an 110AH battery doesn’t sound like much, but its means for me at least the car can stand longer without me worrying about starting it. (Although you’ll notice in the pictures I’ve install cabling for a conditioning charger)

Bear in mind in all these tests the alarm is not activated, therefore you do not know the current drain of the alarm system or whether your fault lies there. If you test all the fuses and find no fault found, I’d suggest extending the wires to the amp meter outside the boot, actually closing the boot/doors/glovebox, enabling the alarm, and watching the meter once sleep is activated again.

Best of luck to anyone else having battery drain woes! It wasn’t that difficult in all honesty, just a little time consuming.



EDIT BTW, i had replaced the FSU, the aux fan prior to the problem developing, and i also there were no codes on the Peake

Last edited by StreetDragster; 9th January 2010 at 12:32 PM.
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post #2 of 118 Old 8th January 2010, 06:56 PM
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ive tried explaining to people in the past how to do this only to get puzzled looks back!! thats a very well laid out post,that should help even the most un multimeter friendly types to check there own cars.

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post #3 of 118 Old 8th January 2010, 07:43 PM
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I am not the only one with this!

New battery was fitted to mine before i bought her, It looked like a dead cell so Euro Car Parts replaced it FOC for me. Car has been fine for a few weeks then this morning, the CLICK CLICK CLICK was back.

I will see if the weather birghtens up and give that ago. I have the big BMW phone in mine which i have been using so I think i will start there....

Thanks for the "How-To!"

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post #4 of 118 Old 8th January 2010, 08:58 PM Thread Starter
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No problems chaps, just happy to be able to give something back to the M5 info-world


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post #5 of 118 Old 9th January 2010, 12:50 PM
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Nice, informative post - thanks.

When my Indy did a pre purchase check on my beast in August one of the first things he asked was "are you ever going to use that phone" - I thought he wanted it. When I replied in the negative he said to disconnect it as they are renouned for draining the system. I did and, touch wood, it's been fine.... firing up first time , every time, even after standing for 3 weeks under 6" of snow and ice.

Thanks again though - even a complete idiot like me could follow that guide!
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post #6 of 118 Old 9th January 2010, 03:42 PM
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Well done and good result !!

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post #7 of 118 Old 16th January 2010, 09:44 AM
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Great post! Would be nice if the next person who does this documents which fuses cause the car to wake back up. That way we could avoid testing those until last.

My car may have a power drain since I installed my Bluetooth retrofit kit. It is either I ran the battery down too far while installing (lots of in/out of the car and testing once I reconnected the battery without starting the engine) ... or I've got a battery draw. I'm going to do this procedure and test the phone and nav systems first. Thanks!
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post #8 of 118 Old 16th January 2010, 10:34 AM
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Great post. Thanks for this..

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post #9 of 118 Old 16th January 2010, 01:28 PM
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Excellent - now I can stop explaining this to people every time someone has a dead battery!
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post #10 of 118 Old 19th January 2010, 05:34 PM
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Nice thread, thanks!
Before repeating all that will just pull fuse for phone (exact same car/age/extras etc) and see how it goes.
Only used it on drive home from purchase anyway...
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battery , drain , motorola , trafficmaster , v50

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