Hello and welcome to JA!!!
I'm Billy and i will help you with this.
First of all, even if vehicle is stationary and engine is off, there are quit a few systems that use electricity (clock, radio, engine control module, CAN bus: the controller area network communicating between control modules, the immobiliser, the alarm, the remote receivers........and many more)
So it is normal that battery is still being used.
But if you suspect that a lot of current is being drawn, or battery is draining overnight, you need to check using the following method:
- remove battery terminal and connect to battery through an ammeter (measures amps)
- remove fuses one by one and put back, and see which one is drawing current the most.
That means look at reading on ammeter, remove a fuse, look at reading again, if it drops, then look on the fuse box cover for the related fuse assignement, and if that fuse should not be working when engine is off (e.g. ABS fuse or headlights fuse...) then you need to check the relevant wiring for short circuit.
That is the easiest way to check for battery draws. But if the battery is still ok, and drawn current does not drain it overnight or few days, then it is normal, as there are multiple systems using power, even if vehicle is at rest.
the battery drained in 5 hrs. yesterday? could not start car?
Then you have a leak.
Proceed as i mentionned earlier (use ammeter, and remove fuses one by one)
i know that ? has to be a large draw. what components are suspect?
Oh, there are lots of electrical components, it could be a door lock solenoid, or a faulty wiring causing a short.
Start the test, and you shall pinpoint the culprit!
this will take some time?
is there any historical data for this problem on the 2003 mini?
Well if it is the first time you do this, i think it will take about an hour, which is not a whole lot considering the amount of electrics on your vehicle.
There are no known recalls, but minis have more than average electrical problems.
Now yours is pretty easy to fix, just follow fuses, and you will get the defective system
And once you get that, you can check the components and wiring of the relevant system.