Mercedes Repair Questions? Ask a Mechanic for Answers ASAP
Hi, the clock running backwards is just an indication that the battery voltage is low. It sounds like you have an intermittent parasitic drain on the system. Electrical drains can be very difficult to troubleshoot if they are intermittent. The shop will need to perform a parasitic drain test on the electrical system to see if there is too much drain on the battery when the car is off. A diagnostic test with the Mercedes Star Diagnosis tester may turn up some codes or events that will point to the problem. The car should have less than a 50 milliamp drain on the electrical system when everything is turned off. If the drain is more than that it will eventually kill the battery.
Let me know if you have any questions.