I took my 2017 GLA in today for overheating. It ended up being a problem with my belt and thermostat. Mercedes also said my starter battery and auxiliary battery failed test. However, I have never had any known issues with my batteries. No messages or lights have ever shown on my dash and my car has never died. Is it necessary to replace both batteries?

Ask for the battery test print-out report and ask the service tech to explain why the batteries failed despite the car operating normally.