Printing device operable with power from battery and external power source

A printing device configured to be connected to an external power source capable of outputting an electrical power corresponding to one of a plurality of voltage values, comprising:

• a power controller configured to:
• obtain the plurality of voltage values from the external power source;
• and
• set an amplitude of the electrical power to be output by the external power source based on the plurality of obtained voltage values;
• a print head with a particular rated voltage value configured to perform printing on a printing medium using an electrical power supplied from an electrical power supplying source, the electrical power supplying source being one of the external power source and a battery charged by the electrical power supplied by the external power source;
• a USB port configured to be connected to the external power source with a connection compliant with a USB standard, the electrical power being supplied to the print head and the battery from the external power source through the USB port;
• and
• a controller,
• wherein the controller is configured to perform:
• obtaining a power source voltage value which is the voltage value of the electrical power to be output by the external power source set by the power controller;
• comparing the power source voltage value with the rated voltage value before the electrical power is supplied to the print head;
• when the power source voltage value is larger than the rated voltage value, determining the battery as the electrical power supplying source to be used to supply the electrical power to the head;
• when the power source voltage value is equal to or less than the rated voltage value, determining the external power source as the electrical power supplying source to be used to supply the electrical power to the head, and
• after the controller determines the electrical power supplying source based on whether the power source voltage value is larger than the rated voltage value, causing the electrical power supplying source to supply the electrical power to the head,
• wherein the print head is configured to perform the printing using the electric power supplying source determined by the controller.