On-board power system for a vehicle comprising: - a first system zone with a first voltage source and a first group of electrical energy consumers, - a second system zone with a second voltage source and a second group of electrical energy consumers, - a disconnector arrangement, wherein the disconnector arrangement is connected in a first connection area to the first system zone and is connected in a second connection area to the second system zone, and wherein in a disconnection switching state of the disconnector arrangement the first system zone is electrically decoupled from the second system zone and in a connection switching state of the disconnector arrangement an electrical connection is established between the first system zone and the second system zone, - a decoupling switch arrangement in association with the second voltage source, wherein in a decoupling switching state of the decoupling switch arrangement the second voltage source is decoupled from the second system zone and in a coupling switching state of the decoupling switch arrangement the second voltage source is coupled to the second system zone, - a DC-DC converter, wherein, in the connection switching state of the disconnector arrangement, the second voltage source can be charged by means of the DC-DC converter in the decoupling switching state of the decoupling switch arrangement by means of the system voltage present in the second system zone, wherein an output connection of the DC-DC converter is connected to a line section connecting the second voltage source to the decoupling switch arrangement. characterized in that an input connection of the DC-DC converter is connected to the second system zone or/and the second connection area of the decoupling switch arrangement, - a first system zone with a first voltage source and a first group of electrical energy consumers, - a second system zone with a second voltage source and a second group of electrical energy consumers, - a disconnector arrangement, wherein the disconnector arrangement is connected in a first connection area to the first system zone and is connected in a second connection area to the second system zone, and wherein in a disconnection switching state of the disconnector arrangement the first system zone is electrically decoupled from the second system zone and in a connection switching state of the disconnector arrangement an electrical connection is established between the first system zone and the second system zone, - a decoupling switch arrangement in association with the second voltage source, wherein in a decoupling switching state of the decoupling switch arrangement the second voltage source is decoupled from the second system zone and in a coupling switching state of the decoupling switch arrangement the second voltage source is coupled to the second system zone, - a DC-DC converter, wherein, in the connection switching state of the disconnector arrangement, the second voltage source can be charged by means of the DC-DC converter in the decoupling switching state of the decoupling switch arrangement by means of the system voltage present in the second system zone, wherein an output connection of the DC-DC converter is connected to a line section connecting the second voltage source to the decoupling switch arrangement.