ResMed's DC Converter allows you to operate any S9 CPAP/BiLevel Machine (with or without the H5i Heated Humidifier and ClimateLine tubing) from a 12V or 24V DC Power Source like those found in many cars, boats, trucks and other vehicles. The total length of the cord is approximately 7.5 feet. A DC Adapter Cable, as shown, with "alligator" clips is also included for powering your S9 machine directly to an external battery.