An electrical device, such as a battery charger, a method for operating an electrical device, a method for charging a battery, and a software program for operating the electrical device and/or the battery charger. In some aspects, the battery charger is capable of charging different types of batteries and capable of operating on alternate sources of AC power or alternate sources of DC power. Also, the battery charging circuit will not operate if one of the power source, the battery, the power switch means and the control means (including the microcontroller) malfunctions. In addition, in the battery charging circuit, the battery under charge enables the operation of the battery charging circuit.