My 2006 Touareg is suffering unexplained battery drain after being left a couple of days without use. The battery is completely dead with even the clock stopped and the key unable to be removed from the ignition. The battery was replaced when tis was first a problem some 18 months ago but the problem persisted. VW dealer diagnostics say they cannot find a fault despite having been in to them four times. My roadside assistance company is now saying they will not come out to start - [too many call outs for the same problem]. Help!