Have Blue Ox hitch for toad

Brake Buddy will send you a free power kit. They started doing that a number of years ago when "cigarette lighters" became "convenience outlets." BB found their units didn't work right with the new outlets and the easiest thing to do was furnish the kit. It's terminals, a fuse, quality wire, and a metal outlet socket with bracket. You could connect such a kit to the battery and then disconnect the Smart Car's battery terminals.

We have several OP's here who tow Smarts, so you'll likely have some specific help soon.