First of all ........ get used to the idea that you never can be certain that the M3W brings you home without breaking down.
But that’s also one of the charmes from a M3W !

Back to the problem.
It’s a brand new car, so could be not all bolts and nuts are correctly tightened.
When you drove all OK. Stopped the car and after the picnic it wouldn’t start anymore.
Lots of noise, same as you half half dead battery when solenoid getting in and out (from what I understand your description).
I didn't read that you say the starter is turning the engine over. Correct ?

Could it be the battery cables are not correct tightened to the battery ?
Because when you drive you don’t need much Amps for the sparks plugs and keep other appliances running.
You still have 12.1Volts as you describe because there are no Amps needed to show that.
But …. if you want to use the starter you need a lot of Amps, which can’t flow freely if the connection between the battery and the starter is not 100% tightened.

If I needed to make a bet …………..

Last edited by Laurens; 07/06/20 10:48 AM.

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