How Does a Faulty Auxiliary Battery Affect My Vehicle's Performance?
An auxiliary battery malfunction affects your vehicle's performance by causing errors in the car's electrical systems. 
If you have a faulty auxiliary battery, your car's electrical components and safety features will stop working. This includes; Entertainment system, GPS, audio system, PDC sensors, Blind Spot Assist, and Lane Keeping Assist. The worst is that the car may fail to start or stop.

What Will Happen if the Auxiliary Battery Malfunction Appears on the Dashboard?
The auxiliary battery experiences wear and tear like other car batteries. This causes the battery to malfunction. A warning message appears on the dashboard, alerting you to act fast.
You should replace the auxiliary battery if your Mercedes starts normally, but the auxiliary battery malfunction message appears on the dashboard. Also, if this warning message appears on the dashboard, your car's electrical components will fail since the auxiliary battery powers them.

​What Should You Do When You See the auxiliary Battery Malfunction Indicator on Your Dashboard ?
The auxiliary battery supplies power to your car's entertainment system. This means you won't have an entertainment system if the auxiliary battery is faulty. The battery also powers PDC sensors. So, the radar system will be affected when the auxiliary battery malfunctions.
Last but not least, the auxiliary battery is a backup to the main battery. If the main battery fails, the auxiliary battery can start the car. It's a pity if both batteries fail because you won't be able to use the car.
You don't want to risk an auxiliary battery malfunction indicator on your dashboard. It's best to act fast by having a mechanic check it out and advise the way forward. The last thing you want is a Mercedes with stalled operations.