A method for operating a field device of industrial process and/or automation technology, wherein the field device, at least at times, is supplied with electrical energy from an energy source. The minimum voltage requirement of the field device is ascertained, and, from the ascertained minimum voltage, a supply voltage value is ascertained, and the field device is supplied, at least at times, with electrical energy, whose voltage is below, or essentially equal to, the ascertained supply voltage value.