Abstract: The invention relates to a method for operating an on-board electrical network (4) of a motor vehicle (2), with a first voltage circuit (I) and a second voltage circuit (II), the first voltage circuit (I) having a first operating voltage which is higher than a second operating voltage in the second voltage circuit (II), the first voltage circuit (I) being connected to the second voltage circuit (II) via a DC-DC converter (8), and the first voltage circuit (I) having a battery (10) and the second voltage circuit (II) having a main battery (12), characterized in that the second voltage circuit (II) has an additional third auxiliary battery (14), and wherein by means of a changeover switch assembly (18) components of the motor vehicle (2) are supplied with electrical energy from the main battery (12) and/or the auxiliary battery (14), and in that the main battery (12) is disconnected from the second voltage circuit (II) by means of an isolating switch (66) during a startup mode.

Abstract: The invention relates to a method for operating an on-board electrical network (4) of a motor vehicle (2), with a first voltage circuit (I) and a second voltage circuit (II), the first voltage circuit (I) having a first operating voltage which is higher than a second operating voltage in the second voltage circuit (II), the first voltage circuit (I) being connected to the second voltage circuit (II) via a DC-DC converter (8), and the first voltage circuit (I) having a battery (10) and the second voltage circuit (II) having a main battery (12), characterized in that the second voltage circuit (II) has an additional third auxiliary battery (14), and wherein by means of a changeover switch assembly (18) components of the motor vehicle (2) are supplied with electrical energy from the main battery (12) and/or the auxiliary battery (14), and in that the main battery (12) is disconnected from the second voltage circuit (II) by means of an isolating switch (66) during a startup mode.