what is draining my battery???

[Rorym2010]

hi peeps ive just had a new battery on my 89 316i and after leaving it for 5 days it was completely drained ive checked all the obvious things like interior lights but cant seem to find whats draining it also when its idleing my interior lights and headlights pulse ive been told this could be down to a bad earth but cant find where the earth is bad is this common and what can i do to rectify these problems cheers in advance

[johnl320]

Sounds to me like your diode pack in the alternator is breaking down, could cause the pulsing and the battery drain whilst not being used.

[Grrrmachine]

I love it when a plan comes together. I only wrote this today:

http://www.e30zone.net/e30zonewiki/index.php/Battery

You'll find links to the Charging section in there, as well as a way to test for the drain using a simple multimeter, and links to all the Wiring Diagrams.

[aimlessrock]

Grrrmachine...that battery in the boot manual is just what i have been after..very good.

I hadn't realised that the cables needed for a cabby was slightly different.

excellent stuff..

[milescook]

I love it when a plan comes together. I only wrote this today:

http://www.e30zone.net/e30zonewiki/index.php/Battery

You'll find links to the Charging section in there, as well as a way to test for the drain using a simple multimeter, and links to all the Wiring Diagrams.

I pity the fool who buys a new battery then that goes flat too

Never knew about battery load testing or the fact its an actual service! Isn't that a bit over kill? Still I've learnt something. I also learnt the hard way - good point for the wiki maybe - not having your instrument cluster plugged in means your alternator won't charge as the battery light circuit is broken! Slightly off topic tho...

[Rorym2010]

have just purchased a multimeter will test the alternator as soon as it comes can a bad earth cause the battery to drain? also buying a new battery was a must as the old on was too low on cca have bought a heavy duty battery for 50 squid with a 4yr warranty so cant complain

[milescook]

Absolutely to getting a good battery with warranty for peace of mind.I nearly replaced my new one from advice I initially got tho! Nothing wrong with it in fact its up for sale

[Brianmoooore]

Sounds to me like your diode pack in the alternator is breaking down, could cause the pulsing and the battery drain whilst not being used.

[Billwill]

have just purchased a multimeter will test the alternator as soon as it comes can a bad earth cause the battery to drain? also buying a new battery was a must as the old on was too low on cca have bought a heavy duty battery for 50 squid with a 4yr warranty so cant complain

No, a bad earth will not cause the battery to drain; a short or semi-short to earth can be a problem though.

I go along with suggestions of replacing the diode pack in the alternator.

[HJG-E30]

Mine used to drain through the aftermarket stereo, as there was no power cut off switch! I put in a switch which connected to the ignition and it's fine now

[twoscoops]

Interesting read this as I am trying to identify the same problem.

[Rorym2010]

do i have to remove the alternator to fit a diode pack?? and the alternator still charges the battery fine would it do that if the diode had gone??? cheers for the info so far

[Rorym2010]

also the alternator on inspection seems to be close to brand new

[johnl320]

Battery can still be charging with this fault, the brush pack can be removed from the back of the alternator without removing it from the car but I'm not sure if this contains the diode pack as well.
The alternator will probably be a refurbished unit which could still be using the origonal diodes if they were healthy at the time of the rebuild.