I fitted a brand new battery to my Roadster and it still drains to fast I would expect a new car and new battery to sit on a driveway or in a garage unattended for a couple of months without starting issues.
Given that the S5 is a new car it shouldn't be suffering age related battery problems.
Sitting on a battery conditioner or isolating the battery isn't an acceptable answer, more work needs doing at the factory to get to the bottom of this.
