Method for operating a wireless field-device network

A method for operating a wireless field-device network that includes a plurality of battery-operated field devices, wherein each field device is configured to determine, set, or determine and set a process variable, and to transmit and receive the process variable wirelessly within the field-device network via a first radio module of the respective field device, wherein each battery-operated field device is also configured to determine an expected remaining running time based on a current charge state of a battery, and to wirelessly transmit and receive the expected remaining running time within the field-device network via the first radio module, wherein each field device also has a second radio module for wireless data transmission with a superordinate unit not belonging to the field-device network, the method comprising:

• wirelessly transmitting the process variable and the expected remaining running time based on the current charge state of a battery from each field device to the other field devices within the field-device network so that the process variable and the expected remaining running time of the other field devices of the field device network are stored in each field device;
• activating the second radio module of a field device which has a longest remaining running time to be expected, and deactivating the second radio modules of the other field devices within the field-device network so that the second radio module of only the field device which has the longest remaining running time to be expected is active and the second radio modules of the other field devices within the field-device network are deactivated;
• and
• wirelessly transmitting the stored process variables, or at least a subset of the stored process variables, of the plurality of field devices of the field-device network stored in the field device having the active second radio module to the superordinate unit via the second radio module of the active field device.