Something’s draining my battery...

[Murt97]

I’m in the process of replacing my voltage regulator, but as I was doing this, I noticed something strange with the battery...

I disconnected the negative terminal for the battery, but when I reattached it moments later (as test) there was a small spark, indicating that something in the car is draining electricity from the battery (everything was turned off to my knowledge). I’m guessing there’s a short circuit somewhere...?

Any help?

Thanks.

[Brianmoooore]

The car uses a small amount of electricity, even if everything is off. There's also a small surge when you reconnect which will make a small visible spark.
If you still have concerns, get a meter on a current range on it, and measure the drain.
The way to do this, to avoid the surge, is to connect the red lead of your meter to a reliable body earth with the battery still connected, but with the neg. terminal loose, place the pointed probe of the black meter lead vertically downwards into the top centre of the battery neg. pole, then lift the clamp up away from the pole, just enough to break contact.

[boiliebasher]

I had a similar issue and checked the resistance on all the fuses with the battery connected.
One in particular, I think it was some sort of interior or boot lighting iirc, was constantly draining power so I just pulled that fuse.
Bit of bodge but it made my battery last for weeks at a time whilst the car was standing.
Before a few days at best and it would be drained

[Brianmoooore]

I had a similar issue and checked the resistance on all the fuses with the battery connected.
One in particular, I think it was some sort of interior or boot lighting iirc, was constantly draining power so I just pulled that fuse.
Bit of bodge but it made my battery last for weeks at a time whilst the car was standing.
Before a few days at best and it would be drained

You had a fault draining the battery. OP hasn't mentioned anything like that, or any other problem - just an observation of a small spark, which is normal.

[Murt97]

I had a similar issue and checked the resistance on all the fuses with the battery connected.
One in particular, I think it was some sort of interior or boot lighting iirc, was constantly draining power so I just pulled that fuse.
Bit of bodge but it made my battery last for weeks at a time whilst the car was standing.
Before a few days at best and it would be drained

You had a fault draining the battery. OP hasn't mentioned anything like that, or any other problem - just an observation of a small spark, which is normal.

As it turns out I’ve fitted a new battery in for a couple of weeks ago and after recently taking a 3 day break from driving my car, the battery is completely flat. So it seems there is something draining the battery after all. I’ll try checking fuses tomorrow... are there any other possible causes common to E30s? Maybe a short circuit?

[biffer]

If you'd left a door or boot-lid open when re-connecting battery you'd get a spark.
My car has a 65ma drain, half of which is through the SI board in the dash cluster.

[Brianmoooore]

Short circuits are easy to find - just look for the source of the plume of smoke and the glowing wires.
Don't guess. TEST. Get a meter in there as I described.

[mark_i]

the key point is to measure and report the amount of current drain with ignition off.
as I recall, the clock, radio, alarm, OBC, and cluster can draw up to 30mA.
I have had defective alternator diode packs causing battery drain issues.