You state that .5 amp draw is normal. It is only normal in the off position where .25-.5 amps is for the memory in the computers and radio.On the accessory position a lot more comes into play.There is a toad charge relay available to work around this issue or disconnect the battery while towing.I have towed my Edge for 4 years and follow the manual procedure with no problems. If you want some real fun tow a Jeep as they do not have an accessory position only ignition on.