That really has nothing to do with itself state or condition. I've had a battery fail in less than a year. The one in my M5 is ten years old. I replaced the original factory battery in my X5 at over eight years old five years ago. You need to perform a proper load test or at least disconnect the battery and check the voltage after five minutes.

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8/2011 X5 xDrive35d Sport, Black Sapphire Metallic, Black Nevada Leather, Fine Burr Walnut Trim
2/2001 M5, Jet Black, Exclusive Complete Black Walk Nappa Point Heritage Leather, Black Cubic Trim