Why doesn't the stop-start function work on my car?

The stop-start, function on my two year old Mercedes-Benz SL350 AMG seems to work on a completely random basis. Some days it becomes operative after a journey of a mile while on others it will refuse to work. Is this a fault?

Asked on 27 April 2015 by mercedessl

Answered by Honest John
Reads as if the battery has lost some of its capacity to hold a full charge and that's why the system appears to be erratic.
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