Flat battery

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Rodent
Joined: Mon 22 May, 2017 08:34
Posts: 24

  Z3 roadster 2.2i

Flat battery

Post by Rodent » Sun 28 May, 2017 20:07

Went out to my 2.2 z3that I've now owned for a whole week, and found that it wouldn't unlock on the remote. Turned out the battery was flat......actually flat is in understatement. It read 0.6v on my multimeter, I've never seen a battery so flat.
I've had it on a battery charger all day and I also checked the voltage at the battery when charging off the alternator, this was exactly 14v. at idle.
I don't think anything was left on overnight so I'm a bit confused. Maybe the battery is dead.
Are there any known offenders when it comes to draining battery's? My thinking is that the battery is knackered as I've never seen such a low voltage (0.6v)

therealdb1
Joined: Tue 25 Jun, 2013 22:47
Posts: 247

  Z3 roadster 2.0

Re: Flat battery

Post by therealdb1 » Sun 28 May, 2017 22:57

Usual suspects are boot light staying on with the boot shut or seat motors trying to run when the seat is at the end stop, or in fact almost anything electrical.
From your posts on here so far it appears that the car has been starting and although modern batteries fail in a Tommy Cooper fashion (just like that!) it is normally only a single cell that goes down so it would still read 10V or so. They also tend not to recharge fully.
If you have access to an ammeter capable of measuring a few amps, connect the earth terminal to the charged battery and use the ammeter to complete the circuit between the positive battery post and the red lead. DO NOT TRY AND START THE CAR LIKE THIS!!!!
At least you will be able to see if there is an excessive current draw which is flattening the battery.
Unfortunately it is then a process of logical elimination to find the culprit, some people pull fuses one at a time others put a camera in the boot when it is closed or check that the seat adjustment switches are not stuck etc.
Without having the car to hand to experiment with you are on your own I'm afraid.

Rodent
Joined: Mon 22 May, 2017 08:34
Posts: 24

  Z3 roadster 2.2i

Re: Flat battery

Post by Rodent » Mon 29 May, 2017 06:52

Thanks very much therealdb1,
Now that you mention it, when i got the car started, there was an intermittent dull click coming from under the passenger seat about once every 5-10 seconds. I moved the seat forward a little and the noise stopped. I think you may have diagnosed the fault 'long-distance' :)
I'm still mystified by the battery voltage. It could be an old battery, but as it lives in the boot, it looks like new!
I think my meter can measure amps, i just need to figure out how to use it properly.

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