When getting my battery tested for an issue in this post, the mechanic noted that when my Ford's "quickclear" windscreen heating element was activated and the engine running, the voltage coming from the battery dips, whereas this doesn't happen with other accessories.
The voltage dipped and continued to decrease. You could see the headlights dim, and if the blowers were on the speed decreased as you could tell by the sound. Using another accessory, for example the rear window heater only caused a momentary dip, and then the voltage stabilised.
Is this normal behaviour for the heated windscreen? The mechanic was convinced this was abnormal and should be looked at. Also, if there is a fault with the windscreen, is this likely to cause any battery drain when the car is off?