Im having the same problem....hmm is this usual?? Turn the key it cranks for 10 second no start, then let off and try again starts right up..only happens once in a blue moon.... however, doesnt seem like the symptoms of a bad battery.

 

maybe lack of acid water, bring the car to autozone and check~
also check the cable too~ the dealer said my (+) size cable was loose and need to replace... but i believe you can just tight it back....

 

These cars are very voltage sensitive. If your battery is showing less than 12.5 volts at rest, things just won't work correctly.

 

New to this German stuff lol When my Camaro breaks i can usually fix it with some part i find at home lol Love that 1950's Tech.