Stop worrying about parasitic draws and do one of two things - either pull the battery ground if you are going to be parked for more than a couple of days (it's right above the accelerator pedal) or install a Tric-L-Charge device. The Tric-L-Charge, in conjunction with your house batteries and charger (solar or conventional) will keep your chassis battery at full charge.
You should convince your dealer to replace the original battery as it probably below specs. Mercedes uses an AGM battery for the chassis battery and while pretty bulletproof, it can be damaged. You can find them locally if you prefer to change it yourself.