Power drains over night

I recently had to replace my alternator after the car went into low mode. It was replaced and I experiencing overnight battery drainage. I replaced the battery eight months ago. The car was tested on the BMW monitor there show no problem. Auto electrical specialist also checked the car with the battery negative off on the fuses and showed 0.18. I have full history service on the car. And when you remove the negative terminal from the battery and leave it overnight it is okay and its starts if I connect it but if I put the terminal back I have sparks on it. Please help me!