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The error message “Backup battery fault” indicates that there is a fault in the backup battery of your Mercedes.
Failure of the backup battery: the task of the battery
First of all, you should know what function the backup battery has in Mercedes:
- In addition to the large battery, which is responsible for all electrical devices inside and outside the vehicle, there are usually two other batteries.
- An additional, small battery is used to support the automatic start-stop system. It takes over the power supply when the engine is started in order to prevent a voltage drop. If this backup battery were faulty, you would receive an error message such as: “S/S is faulty”.
- You have a third battery in vehicles with electric gear selection. This is the so-called backup battery. If there is a problem with it, your car will display the message “Backup battery faulty”.
- The error message can occur not only in vehicles that actually have such a battery installed. Some models, such as a C-Class 205 series built in 2015, have a module with a few capacitors instead of a backup battery. The error message can also be displayed in these vehicles.
Battery error message: you have these options
As is so often the case, you can do it yourself, but it is not advisable. A loss of warranty is just one of the possible consequences.
- Without a diagnostic device, you cannot clearly determine the problem behind the message. Cable breakage, software error, defective or discharged battery – all are possible causes.
- If the battery is discharged, you can theoretically charge it yourself. However, suitable chargers are usually expensive and the purchase is hardly worthwhile.
- If you receive an error message, you should therefore make the journey to the nearest Mercedes workshop. This is especially true if you have a warranty claim.
