Wolfgang,
As has been said on the S1 and S2 a couple of common starting issues have been noted. Firstly the Odyssey battery, a gel type, often shows the right voltage but fails to kick out enough amps to start the beast. I have replaced 2 in my ownership of a S1. You didn't mention it in your symptoms but a clicking would be heard when pressing the starter button. Also the starter motor itself is prone to failure, I have had mine replaced this year and it is a world of difference, like a new car. Immediate start every time, with battery in low or high charge state. Another issue which arose for a S1 owner some years ago was the switch at the clutch pedal. As you know the pedal has to be depressed to start but heat soak from the engine had damaged the switch at the pedal preventing starting. Already mentioned was the uprating, by most owners of the starting fuse, early owners had this done after fuse failure. Would think yours is already sorted. Hope some of this helps.
Dave
