Hi
Can anyone help with a battery drain problem? My Mother has a N plate BMW 328 Cabriolet auto, which has (since purchased and not from new), refused to start after say a week of non use as the battery is completely dead? BMW (several dealers) and auto electricians seem unable to resolve. The car has had numerous batteries (probably 10 in the last 8 years) and possibly an alternator or 2. I imagine that there is some kind of drain and that this could be checked by breaking the circuit to the battery and putting an ammeter in that break in the circuit and seeing what sort of current was being discharged. The car has a serious factory alarm which seems to alarm itself if the car is left for a few minutes and a tracker. What would be a normal drain in amps for a car like this? Some people have said that with an alarm and a tracker it would be likely that the battery would not hold up for more than a week but I find this hard to believe.
Many thanks
Kevin
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First, check obvious things like lights staying on esp. the boot - climb in and shut the boot lid (ALWAYS ALWAYS ALWAYS do this with an assistant) if the seats don't fold down for access. Check also that the ignition switch is actually turning the accessory circuit off.
Less than 25mA quiescent current is acceptable. Over 50mA is way too high. Most OEMs aim for 20mA or less.
Measure the quiescent current with the car 1)unlocked but make sure that everything is turned off and 2)locked and fully armed - you may have to weight down or tape the bonnet switch(es) to make it think the bonnet is shut.
In both cases monitor the current over 30 minutes as the circuits may switch off sequentially.
I suspect the tracker or a boot light sticking on, but am surprised a technician cannot find where the current is going (even BMW have problems getting well trained techs though!!)
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hi
I dont like the sound of "climb in the boot"
--
(iam not a mechanic)
Martin Winters
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Thanks!
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Measured this exact car a couple of years ago and got two readings , initially 1.2 amps and 1 minute later it dropped to 140 milliamps but only after I removed the rechargeable torch from the passenger glove bos. This was faulty and was drawing extra 200 mills and was quite warm. Car was ok after that but be aware of the auto dim interior lights not going off properly. Good Luck. Rgards Peter
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Forgot, this is not including the tracker. Peter
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