Oh you have it?

And how does it work? Do you feel it when the motor is launching, does it start everytime like if you started your motor, or is it quite silent and vibrationproof?

I know you can't beat it, the time you hit the clutch it starts...so when the gear is engaged it has started.

I assume it does not work when the motor is cold.

However, doesn't it hurt the life expectancy of the battery, to constantly start/stop/start/stop?

I think the Mercedes systems uses a special alternator-starter (alterno-démarreur in French) that also helps launching the car from stillstand, but I don't know if it is this more complex system that will be used in the B-Class or if it's reserved for bigger cars.