My car lose electricity. What can make that happen ?

The alternator has been checked and it is OK.

i bought the car from a used car dealer in Montréal. When the problem started, i contacted a specialist (mercedes garage) to check it. the scanner report didn't show anything, so I tried to replace the battery to see if that would work. However, the problem is still there....

copy and paste the link,maybe this will help.watch video IDEO]How to Test and Find a Parasitic Battery Drain … 14:57 www.youtube.com/watch?v=zdIKNnwEjIs

Thank you for this, i will show it to my guy at Mercedes and see what comes out from that.

something is draining the battery,what i don't know,but the mechanic at MB should very well be able to find it.