Than you for your question, my name is Steve and I am a fully qualified vehicle technician with over thirty years in the trade, hopefully I can help.
The message you are getting is indicating that the auxiliary battery voltage is too low. As well as the main battery on your Mercedes you have an auxiliary battery which powers the auxiliary components. The problem may be that the auxiliary battery charging system is not working correctly or that the battery has been drained by excessive use of lights when the vehicle is not running, it may also be due to a poor connection.
The auxiliary battery on your Mercedes is under the passengers floor and you should be able to access it by lifting the carpet. I would ensure there is no damp around the connections which may cause poor conductivity.
The vehicle is quite new to need a replacement auxiliary battery and I would check the other possible causes before replacing it.
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