Battery Draining

[M3KUK]

Hi my 320i Cabriolet is draining it's battery, takes about 2 weeks to go flat then it wont start. I can leave my 325i Saloon for 2 weeks and it's fine, so presume I have a problem.
The car has an alarm, but I have stopped using it for now.
Boot and glove box lights have been removed. Fuse 21 is showing a drain of 0.5A when my tester is plugged into the fuse slot. However, this drops to a steady 0.04A after a few seconds.

According the the Bentley Manual, it powers, Glove box light, torch(not fitted), radio memory, interior light, possibly clock or though it says 'digital clock'. There is some other stuff like tacho, service interval indicator etc but they only work with ign on?

Any thoughts?

[M3KUK]

ps I have fitted a voltmeter and it shows battery charging at 13.6V when running.
The voltmeter itself must drain a bit but it must be tiny as it's an LED type.

[Brianmoooore]

glove box lights have been removed.

If you've just removed the bulb, put it back - the bulb holder can short circuit without a bulb in place.
Turning the alarm off, or not using it, doesn't remove the possibility of it being the culprit.
Intrigued by the 500mA for a few seconds through fuse 27. That shouldn't happen. Also the things that are fed by fuse 27 that only work when the ignition on doesn't mean that they're not the culprit.
40mA through fuse 27 is well within limits, so the problem is either intermittent, or not through fuse 27. Your meter should be connected between the negative pole of the battery and the battery negative lead (removed from the battery) to monitor the total drain, including that taken by the alarm, which could be connected through any fuse or none at all.
13.6 volts is a bit low for a charging voltage as well.

[drakesmith]

My guess is a dead cell new battery needed. Mine did it two weeks and flat. Now winter is coming it will get worse

[Stefan on probation]

Two weeks sounds like an iffy battery if it was within 3 to 5 days then I'd say electrics can you get a loan battery?

[M3KUK]

Thanks guys for replies. I have taped up the glove box connections so that's safe. The battery is/was new about 6 months ago. It is only a mid price one, not a bosch etc. I have a battery tester and last time tested it was ok. I am happy with the 13.6 volts or so as my 325i Saloon reads the same. I know I have to go straight off the battery for the total current drain, that's next step.

[M3KUK]

Cabriolet battery is smaller than a Saloon so can't switch them.

[Brianmoooore]

Cabriolet battery is smaller than a Saloon so can't switch them.

It may be, but should still be interchangeable.
I use an 096 on all E30s, whatever their spec.

[M3KUK]

I only have a small battery with a 65A/h rating fitted. I will try the larger one off my 325i.
According to the Wiki, 0.3A is usual drain current, so not too bad at 0.4A.

[M3KUK]

Sorry got that wrong, usual drain is 30mA which is 0.03A.

[drakesmith]

Take the car to kwick shit for a battery check they tell ya the amps of the battery and if its ok. Believe its free.