I'm sure this thread has saved me a fortune. I had the same problem as others; Megane II stalling and draining battery.
Followed the advice above, cleaned the
sensor and it now runs perfectly - smoother than it has been for ages.
It really, really is as simple as described (a pain to reach in the Megane, but worth persevering). I just cleaned the sensor with a tissue and a finger nail. If I had to do it again I wouldn't even bother unclipping the electrical connector.