While you are waiting consider an automatic battery isolator. Will isolate the battery once it drops below 11.9Volt. You can reset it to start the car. Of course getting to the isolator to press the reset button may be an issue in it's own right. I can get to it an X3 - maybe same as X5.
Low Voltage Battery Isolator - Jaycar Electronics
I have a diesel and it cranks fine via the isolator - well nothing has blown up yet.
Update: nope some issues. Thought better to update rather than leave bad advice standing. The motor cranks as stated but I suspect the isolator drops the voltage to the car electronics enough during cranking to really screw them up. e.g. loss of stability control, loss of electric power steering assist. All fixed on restart though. Removed the isolator and all good again. Next experiment will be to put the isolator not in the cranking circuit from the battery but in the secondary circuit - the circuit that is probably causing the drain anyway.