R53 not starting/no electrical power

[Kit352]

Need a little help here guys. My wifes mini one has started to have an intermitant no start/no electrical power issue. Sometimes when she puts the keys in the lights work but when she tries to crank the car everything goes out. Other times she gets nothing at all. It might sort itself out a few hours later and be fine or it may need a day or 2. I have some free time to look at it this weekend before she goes out and buys another car and i would like to try and fix it. I will check fuses and power as much as i can but i think the problem lies in either the body control module or the ignition switch. The cars battery tested fine and is fairly new. The ignition switch i think i can check out pretty easily but im not so sure about the bcm. My wife said just before the car started doing thus she was trying to put the window up but it was actually going down which tells me it may be the bcm.
Has anyone had these issues and figured out what it was? Can the bcm be checked with normal tools?

[E-bmw]

I have no experience of BCM or its issues but from the sound of what you are describing I would be starting with the basics.

Undo, clean & put back nice & tight all major electrical connections in the starting circuit.

Battery + & - both ends

Alternator + & -

Engine - to body both ends

[Kit352]

I think i figured it out. The negative battery terminal was pretty poor so it was fixed and all seems fine now. Time will tell. At least the wife is happy now. She has an un natural love for that car.