Labbix, is your car fitted with a tracker?
If so, then thats possibly also killing the battery.
I have the same problem on my Subaru.
When am away for 2 weeks the car really struggles to turn over when parked indoors, and needs a jumpstart.
If away for 3 weeks the car is totally dead and doesn't even turn over.
Car is fitted with an RAC Trackster + from the factory. When the battery is low, I get an alert on the mobile.
It was the RAC mechanic who told me that the tracker needs to lock onto a satellite and once it does it goes into sleep/hibernate mode, consuming far less power from the battery. However when the cars in the garage, with no clear line of sight, it can't lock onto any satellites and therefore is constantly scanning for something to lock onto, which inevitably kills the battery prematurely.
No issues with the D5 as it's used daily even though garaged nightly. Occasionally the D5 is not used over the weekend either with no problems and its fitted with a tracker. I have noticed that if the doors are opened whilst vacuuming the interior, the low battery message appears on the dashboard. Also if the radio is on for a bit whilst cars engine is off or watching tv also gives the low battery warning. Am surprised myself that the battery seems to loose so much power in such a short space of time
MY17 First Edition - 3L Diesel Td6 - Farallon Black - Roof rails,side steps,tints,tow bar,mudflaps,door strips.
MY18 Hse Luxury - 3L Petrol Si6 Supercharged - Santorini Black - Roof rails,side steps,tints,tow bar,mudflaps,door strips,22's,dynamic pack 1,bonnet vents,t.v,dual view,frontcooler,360°camera,rear cooler/warmer,roof vane,black LR badges,wade sensing,door sill plates,boot liner, solar screen,wind deflectors,service plan,tracker,speed camera detector,dual dash cameras,ceramic coating.