My 2011 Agile has two factory 12-volt DC sockets
located in the cab, one by the pull-out cup holder (only powered when engine is
running) and one just below the pull-out cup holder which is always powered.
The MB factory sockets are wired into the chassis battery.
I installed 2 additional 12-volt DC sockets for charging our phones/ tablets/ cameras/etc. I wired the new sockets from the coach battery so as not to put extra drain into the starting battery when we are out dry camping. The additional sockets were installed on the outer sides of the dashboard top vents thus minimizing charging cables clutter hanging from the dashboard and interfering while driving. I opted for 12-volt DC sockets and use plug-in USB car chargers in lieu of surface- mount USB charger sockets for more universal mobile charging approach. Also replacing a malfunctioning USB charger with our setup would be much easier, not so with the surface- mount USB charger sockets.