We tow a 2008 Edge and have not had any problems with a dead battery after I read a thread somewhere that said to go past accessory position until the key stops turning. I have towed for over 10,000 miles like this (many times multiple day traveling).
My Roadmaster Even Brake allows me to monitor toad battery voltage and I have been guilty of forgetting to turn switch completely to the stop and have had to stop and do just that as the voltage does go down quickly with it just in the accessory position.
