The charger is rebranded by BMW and sold at the parts counter. It is intended for vehicles which are stored for extended periods. It appears to be useful to some vehicles that are simply parked for a few days.

You shouldn't have to start the vehicle. If you continually get flat batteries, like deutsch has, then it needs to be fixed, or if BMW can't fix it, you need a charger. If you aren't getting flat batteries, don't worry about it, your vehicle is working as designed.

My 2008 535i had the same basic energy management system. I left it parked for most of the last 16 months, driving it about once every month or so, sometimes less frequently. Before that, it regularly sat at the airport for a week, usually twice a month. Never had a flat battery in almost four years.

__________________
2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue