The first low-voltage switching cell prototype, built around a 40 V GaN HEMT, has been successfully designed, implemented and tested. The switching cell includes advanced functionalities such as embedded switching-cell voltage, current, and temperature measurements, and automatic fault-detection and isolation. All functionalities have been experimentally verified at UPC laboratories. This switching cell has been designed to be a basic module to build scalable and highly-power-dense power converters for electric vehicles operating at low voltage levels, such the dc-dc converter interfacing the traction battery with the service battery.