Some help with battery drain.

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Joined: Sun 16 Feb, 2014 22:28
Posts: 51

  BMW other

Some help with battery drain.

Post by warhammer23 » Sat 10 Jan, 2015 13:42

Finally i got a Z3. It's a 1.9 M44 black from 97 - VIN: LD80120

Some pictures first.

May i ask for some help and patience from you - kinda' long post. :)

When i bought it all was good drove excellent and with a large service history.
150k miles.
Even did a 200 mile trip with no problems, i mean what better way to test drive it.
Very happy.

After 2 days sitting outside, the battery went dead it read 7.5 V.
Called the seller, he said in last two weeks all was good, i'm in Torquay (so no winter here) and he had winter with minus degrees and snow and he said it started every time, as it should have been no doubt in my case also. Ok..

Pulled it out put it on my CTEK MXS 5.0 and charged it.
It's a Bosch Silver 60 Ah - but don't know how old it is.
Now it has 13.42 V (fresh out of the charger).
The charger said the battery is ok that it will hold a charge.

Put the battery in, car started with no problems or codes etc.
The alternator has on idle 14.15V
Turned everything on : lights, high beam, signals, air, hazard, radio etc - it had 13.94 V so it's safe to say it's a log way until 13.5 V the minimum.
So the alternator is good. Also no indicator in the dash nothing.

Let the battery in the car - recorded the time and had 13.11V.
So from what i know it should be 100% at 12.72V and go from there when i get back from work (will take my other car) and measure again.
So if i have a big drain in a few hours then there is something.
Did some searching on the internet, recommended to remove the trunk bulb.
Did that.

I noticed that the central locking does not close the trunk.
And the pin from the driver's side get's stuck but the door closes and opens.
All the fuses look ok.

So if i may these are my questions:

1. Could a battery go dead in just a day and it is just bad timing/bad luck? (will test it further so see if it will hold its charge on its own in the house, i mean it should not drop in a few days)

2. More on this, what should be the normal drain ? xx.yy V .. found somewhere it should be like 50 mA so that is 0.05 V per hour? per day ? or ? Because i have a small multimeter i can only measure at the battery.

3.I also have this - what's this. ? Can i remove it ? - i hate electronics ! :) The only problem is that i don't know if it will cause any problems if i interfere i mean is it OEM (?)

4.Could it be the central locking ? because it get's stuck and does not close the trunk and doesn't lift the pin on the driver side ?

5.If i remove the fuse from the central locking - any problems ? I don't mind if i have to manual open the car - i just want the car to run and no more battery drain.

6.The alarm i don't know if it works, needs a new battery in the remote. Can i remove the alarm system just pull the fuses or the ECU & EWS will go berserk if i do this ?

7. At the MOT will they test the alarm system i mean if i remove it will they care ?

8. Also have a CD changer, again can i remove the fuse for piece of mind?

9. Electric seats ? Can they do this i mean i just adjusted them once.

If it was up to me i will remove all electronic commodity but i don't know how the ECU/EWS will react and if i pass MOT in a few months.
So yeah, for now i will monitor the battery and drain and see if the trunk bulb did it.
If not i will remove the fuses from the central locking.
But further than this what should i do more ?

Any input is of great help.
Kind regards,

Joined: Fri 09 Jan, 2015 19:46
Posts: 26

  M roadster S50

Re: Some help with battery drain.

Post by eahornel1 » Sat 10 Jan, 2015 15:14


Joined: Sun 16 Feb, 2014 22:28
Posts: 51

  BMW other

Re: Some help with battery drain.

Post by warhammer23 » Sat 10 Jan, 2015 15:47

Yeah could be this i will rule the battery after i will measure its drain at every 24 hours to see exactly what it happenes.
No alarm just locked by central locking and i removed the trunck bulb.

And for reference what is a normal period until the battery goes dead. Let's say 2 weeks is a good number that the car should start no matter what?
Because i need a time refference to see what is an average of autonomy until the battery goes dead.
My e34 for example would last even 2 months but can't compare them there, the z3 has more stuff on it.

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Joined: Tue 20 Nov, 2012 20:08
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  Z3 roadster 2.0

Re: Some help with battery drain.

Post by Topperz » Sat 10 Jan, 2015 16:21

I've left mine many times with the alarm on for 4 weeks+ and it's started instantly on return

Battery was new about 3 years ago

My wife went to work once in her was fine.....she came out at night and the car was dead..... RAC came out,checked battery and it was completely battery.....never another problem

Just my 10 pence worth
The only bad thing about owning a Z3 is bedtime .......boing!! time for bed said zebedee

Z3 cosmos black individual 2.0

X1 /MSport XDrive 2.0d mineral white

Joined: Sun 16 Feb, 2014 22:28
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  BMW other

Re: Some help with battery drain.

Post by warhammer23 » Sat 10 Jan, 2015 16:30

So yeah it seams batteries have their own attitude.
Thank you also.

Anybody regarding the rest like alarm mot if i pull a fuse etc ?
Any experience doing such experiments?
I don't know how well connected the ecu is ews with the central locking and alarm for example.

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Robert T
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Joined: Mon 12 Jun, 2006 11:35
Posts: 10021

  Z3 roadster 1.9
Location: Cheshire

Re: Some help with battery drain.

Post by Robert T » Sat 10 Jan, 2015 21:54

Batteries are an interesting science, and cells in them seem to be able to die at any time, but frequently with a bit of help from some cold weather, however...

You charged your battery and it held its charge well enough to start and run the car, so it does sound like you have a big current drain somewhere.

The boot/trunk light is a common misnomer and people often suspect it because the plunger things on the boot lid don't turn it out - but that is because the switch is in the lock, not the plungers. :wink:

My suspicion is the seat motors - if they stick on, it can rapidly drain the battery. I would hope that just moving the seat so that it is not at the end of its travel would allow you to ensure that the switch has broken the circuit, but you could also remove the fuse(s) to ensure that they cannot possibly drain the battery.

There are a raft of other things that could cause current drain, from shorts in the boot/trunk lid wiring loom to the tilt switch for the alarm sitting in water as well as stereos, phone kits (which is what your doofer with O2 plastered on it is likely to be) and other bits of interesting wiring installed by previous owners.

If you still have no joy, get a multimeter on it and start pulling the fuses one at a time until you find the drain. The car will normally draw milliamps, and it sounds like you have a drain of several amps. Note that the alarm on your car (with the separate fob) does not like having its power cut and the siren will sound if the power is removed - there is a small round key that operates a switch on the siren to silence it - it is a rather involved process to resync the fobs and alarm if the alarm "forgets" them.

Cheers R.
Arctic Silver '99 Z3 1.9 & Black '59 Frogeye 1275cc

Joined: Sun 16 Feb, 2014 22:28
Posts: 51

  BMW other

Re: Some help with battery drain.

Post by warhammer23 » Sat 10 Jan, 2015 21:58

Excellent and many thanks.
My multimeter only supports 200 mA so i will get a more bigger / pro one if all else fails.

So yeah you gave me a lot of new hints and will start the hunt.
Thank you again.

On a second read maybe the trunk could be? do you think because that the lock doesn't work on it i mean i hear the mechanism working but nothing happens.
No matter what, the trunk is open i can't even close it manualy because i am afraid i will break the key that hard it is.(and i only have one master key)

I will take it apart and investigate further besides the monitoring.
So yeah it will be clear i have a big consumption somewhere.

Joined: Sun 16 Feb, 2014 22:28
Posts: 51

  BMW other

Re: Some help with battery drain.

Post by warhammer23 » Sun 11 Jan, 2015 08:48

Last day at 7 pm it had 13.08 v
And i started it for 2 minutes.

This morning at 7 am so that's 12 hours it had 13.05v.
Considering i started it looks good. (plus what small charge the alternator did, maybe none fram what i know at least above 1.5k rpm it starts to do it properly).
Am i wrong? 00.03 v per 12 hours is ok?
Of course i will monitor it further but so far it's promising that the trunck light did the trick and i also removed the lighter (maybe silly but who knows).

Joined: Fri 26 Dec, 2014 19:43
Posts: 6

  Z3 roadster 1.9

Re: Some help with battery drain.

Post by CurlyBen » Mon 12 Jan, 2015 03:12

I had a problem with battery drain which turned out to be the seat motor - you could quite easily hear the relay switching every few seconds (possibly a thermal cutout?).

If you think about getting a new multimeter I'd suggest a clamp meter - great for monitoring battery drain without disconnecting anything!

However if everything's working out at the moment hopefully it'll stay that way!

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Posts: 1276

Location: ACREFAIR

Re: Some help with battery drain.

Post by TaffZee » Mon 12 Jan, 2015 06:54

I have had the same problem, Battery is only 18 months old, after standing for a weekend battery did not even light a bulb up completly dead, I Charged battery and cleaned the terminals and the earth lead in the trunk where it attached to the bodywork (which did show signs of corrosion), been over two weeks now with no further issues..
Image1998 Atlanta Blue 2.8

Joined: Sun 16 Feb, 2014 22:28
Posts: 51

  BMW other

Re: Some help with battery drain.

Post by warhammer23 » Mon 12 Jan, 2015 08:21

Thanks a lot guys.

Yeah for now i will not start the car wait unti 12.72v so no more residue charge. I will be back in a few days with my results don't want to spam here every 12 hours :)

Thanks again.

Joined: Sun 16 Feb, 2014 22:28
Posts: 51

  BMW other

Re: Some help with battery drain.

Post by warhammer23 » Fri 16 Jan, 2015 11:51

It's been a few days, since the bulb removal it drained from 13.25 v very slowly like 0.03v a day, condescending it was still residual charge.
At 12.76 V after what 5 days, i strarted the car.
No problems.
Run it for 5 mins.
Today after 24 hours it only dropped from that to 12.75 V, so still residual and it holds it really good.

So i presume that was the case :)

Many thanks.


Now i only have to fix my boot lock - can't close it neither via central locking neither via key/manually - i turn both sides nothing happens.
Actuator works - i can hear the click and see it move - removed the plastic covers.
The lock inside works.
The only one that seems to be the culprit is the outside key lock.
Any ideas?

Joined: Fri 04 Apr, 2014 01:11
Posts: 8

  M roadster S52

Re: Some help with battery drain.

Post by nachos23 » Sat 17 Jan, 2015 14:00

Here's a thought that happened to me on my 2000 Z3M. I had the same issue start out of the blue.... Took me a while to find it. It was the sub-amp. Once it was triggered to turn on, it would not shut off draining my battery over night. I started running the amp meter in place of fuses and measuring the current draw while car on and off to find issue. Sub amp is located on left side of trunk next to hydrauic cylinder for roof. There is one fuse that controls all those devices (there are actually 2 fues. I think fuse #44 was the one that I detected the drain on... Remove it and see if you get the drain...I replaced mine with an aftermarket 250W sub amp and it's been perfect ever since. If you put the amp meter inplace of the fuse and turn the amp up, you will trigger the sub. it'll draw around 4amps when running... it should immediately go back to a trickle current of less than 20mA when off if I recall. Mine would not shut off once triggered and continue to draw 4A when turned off... See if that helps.

Joined: Sun 16 Feb, 2014 22:28
Posts: 51

  BMW other

Re: Some help with battery drain.

Post by warhammer23 » Sat 17 Jan, 2015 14:10

Thanks for the input.
I will double check this sub amp.

Ia it the one that is on top of the cd changer ?
Or ..?
If so, i don't have it just the cd changer (which i also removed, don't need it and isolated the plugs with electrical tape just to extra piece of mind)

Thanks again.

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