Open the hood and locate the auxiliary battery in the right side of the engine bay.
Remove the 10mm plastic nut from the cabin filter housing.
Remove the 10 mm nut from the top bracket. Lift up the bracket.
Remove the 10mm bolt from the negative battery terminal.
Remove the 10mm bolt from the positive battery terminal. Be extremly careful so that the positive cable does not come in contact with any metal parts.
Remove the old battery and place the new battery in place. Connect the positive cable first. Connect the negative cable last. Spray battery terminal protector on the battery post to prevent corrosion. Install the cabin filter lid.
No programing or coding is required. Once you replace the auxilary battery on your W211 E-Class, the warning message should disapear from the dashboard.