Hi, my name is ***** ***** is way too high. It sounds like you have a voltage regulator fault. You should get the vehicle scanned for fault codes with the Mercedes tester. More than likely you will find fault codes for excessive voltage, not undervoltage. You will probably need to replace the voltage regulator or alternator to remedy this problem.
Overvoltage will cause the systems to shut down the same as undervoltage. What you are describing sounds like a weak battery though. What do you mean when you say there is barely enough juice? Is the rear battery going dead?
When an overvoltage situation occurs the system will shut down to protect them from damage. You need to get the voltage down to the proper range. 14.7V running is about as high as it should ever go.
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