Just a follow up, many people still don't know that the 453 DCT CAN be flat towed at freeway speeds over long distances. When I took mine to the local smart center the service guys saw the tow setup and started freaking out, said the car can't be flat towed, that I would fry the transmission, etc.. When I showed them the pages from the owner's manual supplement they said Oh, I guess you can but be sure to follow each step EXACTLY as described.
I know many people don't want to disconnect the battery but you really need to. Not doing so could cause the ABS or ESP to engage when you don't want it to and cause major issues for you. The only thing I lose when disconnecting the battery is the clocks have to be re-set and the radio pre-sets are lost. I don't use the radio pre-sets as we travel extensively with the car so they are always wrong anyway I turned off the clock display in the radio and the clocks in the dash are easy to re-set using the steering wheel controls.
The only issue I've had is the braking system I use requires a cable that runs from the tow bar to the brake pedal. When the car pushes against the tow bar a surge brake engages and pulls the cable applying the brakes in the smart. When I first installed the cable I pulled it slightly snug which is what the manufacturer's instructions said to do. After driving the car for about a week it went into limp mode on me. Apparently the ABS sensor on the brake pedal is very sensitive and the car thought I was driving around with the brakes on so shut down on me. After adjusting the freeplay in the cable a little and clearing out the codes the ABS was happy again and I haven't had a problem since.