BATTERY ISSUE

[phantom3]

Hi everyone - after two years of literally losing my mind with my beautiful Z3 I really hope you can all help!

I KNOW for a fact this is a very common issue with the Z3 so I am amazed at how few decisive answers there are around for it: the battery keeps going flat and I keep going absooolutely mental whenever it happens.

I have replaced it and it does it. I keep recharging it and it does it within 24 hours. I have replaced fuses, removed fuses, left it locked, left it unlocked...and have no idea as to why it is draining its battery.

I have read about a few thousand postings from people also experiencing this yet still to read one who has found a solution to it...are we all just moaning about it, buying trickle chargers and putting up with this insanity?

HELP!

[colb]

How about fitting a battery master switch so you can isolate the battery and stop anything drawing on it if you cannot pinpoint what it is that is drawing on it?
I suppose you have checked the boot light out as this seems to be one of the main culprits when it won't switch off?

Colb

[Mike Fishwick]

First consider your driving style - is the battery getting a decent amount of charging when in use, and is it having to stand for long periods between being used? A month of inactivity will lose over 20 ampere hours capacity. After being flat, does the battery receive a full charge? Remember that deep discharges will ruin most batteries, whic is why they are excluded from the warranty.

Then measure the discharge current under normal conditions - ie with the engine stopped and everything turned off - it should be 30 to 50 mA.

If the current is higher pull some fuses out one at a time, particularly those for systems which are live when the ignition is off. - typical culprits are seat motors jammed on and after-market stereos, boot light etc. If necessary pull all the fuses until you see the current fallback. If necessary disconnect the alternator and starter motor.

Try these baic things and report back - there are also other, more inaccessible fuses to consider.

[beerbelly]

id bet on the alternator being the culprit

[BladeRunner919]

I KNOW for a fact this is a very common issue with the Z3 so I am amazed at how few decisive answers there are around for it

I'm not aware of it as a common issue at all. In fact it's not a problem I've come across other that when cars have been left for long periods or have some sort of fault.

[Southernboy]

In over 10 years of Z3'ing, I have only ever replaced the battery once...and that was because it literally died...I would have the alternator checked, and that is doing what it should, perhaps you should have a look at the alarm - if you have one... alternately, check the positive lead to the battery isn't somehow in conact with the car body anywhere in it's housing. Check for chafing of the cable insulation...

[phantom3]

Honestly thanks so much everyone for these replies - really appreciate it. I will go through everything again with the meter and double check the stats. I already tried the boot light and the alarm but still no joy - I think I will try the seats fuse actually - that's one I haven't and indeed check the insulation on the wires.

Thanks everyone - I will update you all next week

[Robert T]

Battery problems are fairly common on the Z3, I suspect because many people use them as a second or third car and they are frequently not driven for long periods - if they are left locked with the alarm set, then this will eventually drain the battery. However this does not sound to be your problem - a healthy battery should not go flat for many weeks with just the alarm draining it.

The first thing to establish is what your problem is - do you have a continuous drain on the battery or is the battery not being charged? An ammeter should tell you that. If you have anything more than 10s of milliamps, then you have a drain problem, if not then it may be the charge side.

I have heard of at least one case of seat switches breaking and trying to run the seat motors all the time, so it is worth checking that one out.

Battery life depends on a lot of things, but one big factor is the quality of the battery you fit. The rubbish American thing (not my word - those of the BMW Emergency Service guy!) that was fitted to my car in the factory didn't last 3 years. The BMW Germany one that replaced it is still on the car over 12 years later! And no, I don't run a trickle charger, I just drive the car!

Cheers R.

[Rocketbike]

I just had what looked like a battery or earth problem on mine, which turned out to be the alternator which had gone wrong. Car would drive OK, and then the battery would be dead (no idiot lights etc.) when I went to start it again after it had been parked up a few hours. First sign was loss of central locking when parking the car, and being unable to set the alarm. Diagnstics showed the alternator wasn't putting enough charge into the battery, but I wasn't convinced because the car was so dead. I ended up driving around with a spare battery which I was lucky enough to borrow, (which proved it wasn't that) before I went for the alternator. The alternator was replaced, and all now works fine.

[Mike Fishwick]

I would certainly NOT call the OE battery as 'rubbish' - mine lasted for 12 years. The problem is usually the owners, whose lack of maintenance and ill-treatment usually as rubbish! How many people dump their car in the garage all winter, and never trickle charge the battery? How many never check the cell levels, and only use de-mineralised water to top to top them up?

If you never changed the engine oil or filter for twelve years you would expect problems, and batteries are no different.

Anyway - in this case do not assume that the battery or alternator - or anything else - is the cause, but use logical diagnosis - it is a lot cheaper, and you may learn something in the process. I would first check for current drain, and follow this with a check on alternator voltage (about 14.5 to 14.8 volts with headlamps on) or the other way round.

The frustrating problem about diagnosing forum problems is the usual lack of information - in this case, how old is the battery, what make is it, how many times has it been fully discharged, what the on and off charge voltages are - coupled with the invariable lack of feedback afterwards and the owner's usual lack of even a basic voltmeter.

[phantom3]

Hey everyone - Mike permit me to say I really appreciate the degree to which you explain everything. This week I will be eliminating different fuses. After reading everything I also reckon on it being the alternator.. When the battery has been fully charged, it starts absolutely no worries...then I can drive it and will give it a nice long run...but hours later it is flat...sound like the alternator to you all? Or reckon I'll still figure out something with the fuses?

[Mike Fishwick]

To quote Hercule Poirot, the great Belgain detective: "I suspect no-one, and I suspect everyone!"

You could have a faulty alternator, but you could also have a faulty battery, earthing cables, a faulty starter motor, and a few other things - hence the comment about applying logical diagnosis techniques.

First, you need a decent test meter - nothing fancy, just something which will read up to 20 or so volts, and up to 1 amp - which will enable you to decide.

Ther is a lot of information on this forum about testing for excessive discharge current.

The usual problem with alternators is worn brushes, which can be replaced by soldering new ones into position. This is a lot cheaper than the usual preference of buying an exchange alternator, and although you may find peole trying to sell you a complete voltage regulator and brushes, they are available seperately.

Good luck!