Multiple conditions can determine how deeply discharged a battery can become when the vehicle is parked for extended periods. The weather (especially extreme cold or heat) is definitely one...and things like how many times the new modern features “awaken” from near vicinity of aerials that can pick-up commands etc (like remotes in your pocket/purse as you walk by or near the vehicle awaiting a command to lock/unlock etc).
Click the following link to see the BMW recommended battery charging calendar:
https://www.newtis.info/tisv2/a/en/g...system/2RvCTKq
If you have a BMW (or any car) that sits for extended periods of time...I would highly recommend investing in a BMW (or CTEK) battery charger/maintainer. This way the battery stays charged and prevents it from going into states of discharge...where repeated states of discharge will shorten the life of the battery. A battery maintainer is worth it.