NOVELTY - The method involves adding a preset voltage signal (U-VAR) to a direct current component (U-S) delivered by a direct current to direct current converter (4) with an electrical network (2) that is provided with an electric battery (10). A current (I) traversing the electric battery of the electrical network is measured by searching a current intensity signal corresponding to the added voltage signal to check whether the battery is properly connected to the electrical network, where the voltage signal and the intensity signal are periodic signals.    USE - Method for detecting a disconnection of an electric battery in an electrical system equipped with two electrical networks interconnected by a direct current to direct current converter, for a motor vehicle (claimed).    ADVANTAGE - The current traversing the electric battery of the electrical network is measured by searching the current intensity signal corresponding to the added voltage signal to check whether the battery is properly connected to the electrical network, thus assuring the good connection of the battery of the low voltage network in the motor vehicle even when one of the networks comprises a battery recharged through the converter from other network, and hence assuring the security for the low voltage electricity supply for the automobile electrical system, in a cost effective manner. The method allows a detection device of the vehicle to be reliable, and does not allow the device to disturb electrical components and electrical loads of the networks without increasing the size of the vehicle. The method alerts the driver of the vehicle if the battery is not connected and allows the driver to set up backup procedures for operation of the vehicle to enable the safety of the vehicle without using the low battery voltage.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a motor vehicle equipped with electrical networks.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a electrical system of a vehicle equipped with a detection device.    Current (I)    Direct current component (U-S)    Preset voltage signal (U-VAR)    Electrical network (2)    Direct current to direct current converter (4)    Electric battery (10)