The nominal voltage is a voltage that is specified for voltage sources, consumer devices or tests as the nominal value for normal operation. It is therefore the voltage that a battery, accumulator, capacitor or generator nominally provides and that components, devices and systems require for their specified operation.
The nominal voltage is subject to certain tolerances, which are specified as rated voltages. For voltage sources such as batteries, rechargeable batteries, or the line voltage, the rated voltage is less than the open-circuit voltage, which is reduced by the internal resistance of the energy source when current is drawn.
The nominal voltages of batteries and accumulators are 1.5 V for most zinc accumulators. Lithium cells, the nominal voltage is about 3 V. As for the mains voltage, in Germany it is 230 V for single- phase current and 400 V for three-phase current, in the USA it is 110 V for single-phase current.