NOVELTY - The device (8) has a battery connection (86) arranged for connection with a connection pole of a battery (5), which is carried in a commercial vehicle trailer (2). The device supplies an electrical supply power, which is withdrawn from the battery via the battery connection, to an electronic control device (4) and/or electrical components (40-43) by a supply output connection (84) when monitoring of the electrical supply power that is supplied by a supply input connection (82), obtains fulfillment of a preset monitoring criterion.    USE - Electrical power supply device for supplying electrical power to an electronic control device of a brake pressure modulator, and electrical components e.g. electrical actuatable magnet valves, lamps and sensors, of a brake system and a ride-height control system of a commercial vehicle trailer (all claimed).    ADVANTAGE - The device avoids the need for manual on/off switches, thus simplifying an electrical system and cabling, and avoiding erroneous operation of the switches, and hence ensuring simple operation of the trailer. The device ensures simplified handling of control systems installed in the trailer. The device enables use of manual operating elements of electrically controlled ride-height control without limitation of manual requirements of a desired ride-height position of a loading ramp without the need for attention or activity of a user for ensuring an operating ability.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for an arrangement including an electronic control device and an electrical power supply device.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of a commercial vehicle trailer with an electrical power supply device.    Commercial vehicle trailer (2)    Electronic control device (4)    Battery (5)    Electrical power supply device (8)    Electrical components (40-43)    Supply input connection (82)    Supply output connection (84)    Battery connection (86)