Check the voltage with the car off. Can be done easily with a multimeter from under the hood at the + & ground posts. If the voltage is seemingly higher than 12 volts, even 12.1, likely its a failing battery. It should typically never exceed 12v when new. If it's exceeding 12v now, it likely means that the decreasing electrolyte content is creating a more acidic environment and when running, will actually create a higher than normal voltage system potentially playing havoc with some components. This is a theory and of course, most people replace the battery before you can ever really spend time proving it. But the science is there....

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2006 X5 3.0L - Schwarz Black/Truffle Brown
Stock
But I keep it clean