NOVELTY - The method involves determining a signal value corresponding to battery voltage of a rechargeable battery e.g. lithium/metal hydride battery, supplying energy to a thermal print head. A signal value corresponding to the determined signal value is stored as a stored signal value. Energy delivered from the battery to the print head is changed/increased (498) in response to changes in the stored signal value from a signal value corresponding to battery voltage at a level above threshold battery voltage to a signal value corresponding to the battery voltage at/below the threshold voltage.    USE - Method for operating a thermal print head of a printer e.g. thermal printer (claimed) such as thermal label printer, to print a substrate e.g. thermal printable substrate such as vinyl substrate, thermoplastic polymer film substrate such as multi-layered high density polyethylene (HDPE) thermoplastic substrate, and sheet/fabric substrate.    ADVANTAGE - The method enables the energy delivered to print head elements of the thermal print head to be increased for ink transfer ribbon/substrate combination when power is available from the battery for printing drops so as to provide prints of acceptable quality despite drop in voltage from the battery. The method enables static electricity to be completely discharged from a printed substrate so as to minimize or eliminate risk of damage to the printer from static electricity using an electrical static discharge mechanism.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a thermal printer comprising a computer processor.    DESCRIPTION OF DRAWING(S) - The drawing shows a flow chart illustrating a method for controlling a printer based on changes in battery voltage.    Step for measuring printer voltage (444)    Step for determining whether significant voltage drop is occurred (448)    Step for determining whether significant voltage drop is measured at enough times (452)    Step for switching to alternate power source or turn off printer (460)    Step for changing/increasing energy delivered from battery to print head (498)