The invention relates to a method and a device for operating an electrically assisted exhaust gas turbocharger of a motor vehicle. The device comprises an exhaust gas turbocharger (10) with a first electrical machine (14) which can be operated as a motor and as a generator for driving or providing drive assistance to the exhaust gas turbocharger. The device further comprises a low-voltage electrical system in which a second electrical machine (3) which can be operated as a motor and as a generator and which is torque-transmittingly couplable or coupled to the crankshaft, and an electrical energy storage device (5) for supplying electrical consumers arranged in the low-voltage electrical system are provided. The device further comprises a control device (1) which is configured to control the first electrical machine (14) of the exhaust gas turbocharger (10) in a first operating mode (S3) in order to drive the exhaust gas turbocharger (10) with electrical motor assistance, and to control the first electrical machine (14) in a second operating mode (S4) in order to recuperate electrical energy from the exhaust gas energy via generator operation. The control device (1) is configured to supply electrical energy from the low-voltage electrical system of the motor vehicle to the exhaust gas turbocharger (10) in the first operating mode (S3) and to feed the electrical energy recuperated by the exhaust gas turbocharger (10) into the low-voltage electrical system in the second operating mode without prior intermediate storage.
