Hi and welcome to the forum. The car is packed with sensors used to monitor various things. They all require a voltage to work so if you don't drive the care for a month these sensors will slowly drain the battery. The Mercedes Me app will usually send you an email when the battery falls below a certain voltage level advising you to either attach a battery charger or take the car for a 30-minute drive. Perhaps the Dealer hasn't set this up for you. The car is clever enough to never deplete the battery below a voltage that would prevent the car from starting. If your battery does turn out to be faulty (your Dealer would hook the car up to their diagnostic equipment to confirm battery drain) you can have a free replacement under the 3-year warranty that comes with a new car.