Operation method for an energy storage system of a motor vehicle, wherein the energy storage system comprises several electrical energy storage devices (2-1, 2-2, 2-3, 2-n) and each of the energy storage devices (2-1, 2-2, 2-3, 2-n) comprises an energy storage control device (3-1, 3-2, 3-3, 3-n) for controlling the operation and monitoring the state of the respective energy storage device; wherein the energy storage control devices (3-1, 3-2, 3-3, 3-n) are coupled to each other according to the master-slave principle, such that wherein one of the energy storage control devices (3-1, 3-2, 3-3, 3-n) is set as a master control device adapted to control the operation and monitor the state of the energy storage system, comprising the entirety of the several electric energy storage devices (2-1, 2-2, 2-3, 2-n), and wherein the remaining energy storage control devices are set as slave control devices (3-2, 3-3, 3-n), which each forward data on at least one operating state of their associated energy storage device to the master control device and receive control signals from the master control device, wherein the master control device being configured to receive data on at least one operating state from the slave control devices (3-2, 3-3, 3-n) respectively and to transmit control signals for them, wherein the functionality of a master control is implemented in at least two of the energy storage units and is activatable and deactivatable for execution, respectively, said operation method comprising: monitoring an operation of the master control device; and activating one of the slave control devices (3-2, 3-3, 3-n) in which the functionality of the master control is implemented as a new master control device, if the monitoring indicates that the master control device is no longer operating properly; characterised in that those control devices set up as slave control devices (3-2, 3-3, 3-n) in which the functionality of a master control is implemented but deactivated are configured to read along signals for and/or from the master control device. wherein the energy storage system comprises several electrical energy storage devices (2-1, 2-2, 2-3, 2-n) and each of the energy storage devices (2-1, 2-2, 2-3, 2-n) comprises an energy storage control device (3-1, 3-2, 3-3, 3-n) for controlling the operation and monitoring the state of the respective energy storage device; wherein the energy storage control devices (3-1, 3-2, 3-3, 3-n) are coupled to each other according to the master-slave principle, such that wherein one of the energy storage control devices (3-1, 3-2, 3-3, 3-n) is set as a master control device adapted to control the operation and monitor the state of the energy storage system, comprising the entirety of the several electric energy storage devices (2-1, 2-2, 2-3, 2-n), and wherein the remaining energy storage control devices are set as slave control devices (3-2, 3-3, 3-n), which each forward data on at least one operating state of their associated energy storage device to the master control device and receive control signals from the master control device, wherein the master control device being configured to receive data on at least one operating state from the slave control devices (3-2, 3-3, 3-n) respectively and to transmit control signals for them, wherein the functionality of a master control is implemented in at least two of the energy storage units and is activatable and deactivatable for execution, respectively, said operation method comprising: monitoring an operation of the master control device; and activating one of the slave control devices (3-2, 3-3, 3-n) in which the functionality of the master control is implemented as a new master control device, if the monitoring indicates that the master control device is no longer operating properly; characterised in that those control devices set up as slave control devices (3-2, 3-3, 3-n) in which the functionality of a master control is implemented but deactivated are configured to read along signals for and/or from the master control device. monitoring an operation of the master control device; and activating one of the slave control devices (3-2, 3-3, 3-n) in which the functionality of the master control is implemented as a new master control device, if the monitoring indicates that the master control device is no longer operating properly; characterised in that those control devices set up as slave control devices (3-2, 3-3, 3-n) in which the functionality of a master control is implemented but deactivated are configured to read along signals for and/or from the master control device.