What is the approximate nominal voltage rating of a fully charged nickel-cadmium battery with twenty cells?

A fully charged nickel-cadmium (Ni-Cd) battery's nominal voltage is based on the individual cell voltage and the number of cells in series. Each nickel-cadmium cell typically has a nominal voltage of about 1.2 volts when fully charged.

To find the total voltage for twenty cells in series, you would multiply the number of cells by the voltage per cell. Specifically, multiplying 1.2 volts by twenty cells yields approximately 24 volts. In practical terms, this means the nominal voltage can often be rounded to around 25 volts when considering the voltage rating at a full charge, especially in many applications where some tolerance is accounted for.

Therefore, the correct answer of approximately twenty-five volts reflects the expected nominal voltage for a fully charged nickel-cadmium battery consisting of twenty cells, aligning with standard battery specifications and practices in the industry.