MERCEDES E W211 [2002-2009] How to get to the auxiliary battery? Secondary small battery location. - YouTube
For Mercedes Benz W211 Fiber Recorder Car Aux Optical Fiber Decoder Most Box E Cls Slk Cl S Class Amplifier Adptor Harman Kardon - Battery Cables & Connectors - AliExpress
ORIGINAL MERCEDES BENZ W169 W176 W245 W242 W204 W211 AUXILIARY BATTERY / BACK UP BATTERY (0009829608)