It's an answer not a question! (Arrff Arrff) Perhaps useful for us Sunday Drivers (or less).
My measurement is 36mA, or 0.86Ah/day, or about 50Ah in 60 days.

Test vehicle: 2008 X358
Test Conditions: Once at float with a smart charger, current (via maH) measured over 15hrs.
Battery Condition: Calcium/Good. (was replaced when I bought her 3yrs ago, been kept charged since). But figures might vary.
Why 50Ah/60 days figure? Car batteries are rated in cranking amps not amp-hours. In either case they should never be discharged below 1/2 charge. Ah equivalent rating is just a guess for "1/2 used".

No matter how long you drive, the car's charging system never completely "fully charges" the battery. I can always put (say 5Ah or so) into the battery to get back to "floating charge" with a smart charger. We all know it's bad to leave any car unattended for more than a few weeks. This works to my advantage, whenever my brother goes overseas for more than a few weeks, I AM FORCED to drive his BMW!

Anyway, I suspect these are typical figures for an unattended modern car, not that the X350/X358 is especially "battery-hoggy" at rest. Cheers