The rear offside parking sensor has apparently had a bump and is slightly depressed, being likely to fall further inwards. It now gives false warnings when reverse is selected. I need to reseat the sensor. How do I get at it? Is it necessary to remove the wheel arch shield?

I checked the 12v auxiliary battery today and found that the terminal voltage was 11.9v. The 12v battery only charges, at 13.5v, when the "ignition" is on. This means that if the car is mainly uised for short journeys the essential auxiliary battery may become dischargedsufficiently to lock me out of the car and prevent starting. Has anyone fouind a way of trickle charging the 12v battery? Why can it not be kept charged by the traction battery even when the car is not being used?