A plurality of prongs of a connector box and a plurality of receptacles of a receptor box are electrically connected by mating each respectable pairs together. The boxes are coupled by a mechanical leveraged maneuver. The connecting device then connects vehicular circuits of an electric vehicle including those for auxiliary equipment to a battery-carrying trailer which is to be mechanically attached thereto and allows the electric vehicle to either extend its range, or be rescued from power shortage by electricity supplied by other than batteries onboard therein. The connecting device has a safety mechanism for preventing accidental separation of an electric connection, and for protecting operators from receiving electrical shock.