The SLR runs two batteries, and an auxiliary-battery drain problem is reported by multiple owners: batteries deplete even on the factory trickle charger, and if both go flat the car cannot be opened normally, requiring access through release pulleys in the trunk. Owners describe door scratches from people trying to force the doors when the batteries are dead.
Twin-battery and auxiliary-battery drain quirk
Mercedes-Benz SLR McLaren (C199) · mechanical