Battery pack for supplying power to a field device and for providing an output voltage to the field device, comprising a power source; a capacitor; a voltage measuring device adapted to measure the voltage at the power source; logic means; a voltage converter adapted to convert a first voltage to a second voltage; wherein the first voltage is applied to the current source; further comprising: a voltage regulator having an enabled mode and a disabled mode; control means, wherein the control means is adapted to convert the voltage regulator to the enabled mode upon a signal from the field device; and wherein the output voltage is the second voltage after putting the voltage regulator into the enabled mode and is the first voltage after putting the voltage regulator into the disabled mode; wherein the logic means is adapted to compare the measured voltage at the current source with a predefined limit voltage and to transfer the comparison result to the control means; wherein the control means is further adapted to transfer the voltage regulator to the enabled mode only if the logic means determines that the voltage falls below the limit value and a message from a controller of the field device that the execution of an energy-intensive task by the field device is imminent; wherein the capacitor is adapted to make its stored charge available to the field device at increased power consumption, the capacitor being further adapted to be charged by the second voltage. a power source; a capacitor; a voltage measuring device adapted to measure the voltage at the power source; logic means; a voltage converter adapted to convert a first voltage to a second voltage; wherein the first voltage is applied to the current source; further comprising: a voltage regulator having an enabled mode and a disabled mode; control means, wherein the control means is adapted to convert the voltage regulator to the enabled mode upon a signal from the field device; and wherein the output voltage is the second voltage after putting the voltage regulator into the enabled mode and is the first voltage after putting the voltage regulator into the disabled mode; a voltage regulator having an enabled mode and a disabled mode; control means, wherein the control means is adapted to convert the voltage regulator to the enabled mode upon a signal from the field device; and wherein the output voltage is the second voltage after putting the voltage regulator into the enabled mode and is the first voltage after putting the voltage regulator into the disabled mode; wherein the logic means is adapted to compare the measured voltage at the current source with a predefined limit voltage and to transfer the comparison result to the control means; wherein the control means is further adapted to transfer the voltage regulator to the enabled mode only if the logic means determines that the voltage falls below the limit value and a message from a controller of the field device that the execution of an energy-intensive task by the field device is imminent; wherein the capacitor is adapted to make its stored charge available to the field device at increased power consumption, the capacitor being further adapted to be charged by the second voltage.