| I have had the same issue off and on with my ST4s. Even though all the electrics worked and the battery was fully charged there was not even a click when the starter button was pressed.
It seems that the plastic clip that holds the live feed to the starter motor on is not of the highest quality and sometimes the connection is not the best.
Mine is now held together with a cable tie and has been fine for the last 5k miles. | 
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