Does a battery charger have to have a transformer and a rectifier to produce dc volts?

A battery charger does not necessarily have to use a transformer and a rectifier to produce DC voltage, although they are commonly used in many designs. A transformer steps down AC voltage to a lower level, while a rectifier converts AC to DC. However, some chargers may utilize switch-mode power supplies or other techniques to directly convert AC to DC without a traditional transformer. In those cases, different methods of voltage regulation and conversion are employed.