A hair dryer comprising: a housing; a rechargeable battery pack including a plurality of lithium-ion battery cells, the rechargeable battery pack disposed within the housing; each battery cell having a discharge path; each battery cell having a beginning of life recoverable charge capacity and an in-use recoverable charge capacity; each battery cell further having a state of charge, the state of charge measured as a percentage of recoverable charge capacity; each battery cell further having a state of health, the state of health determined by comparing the in-use recoverable charge capacity to the beginning of life recoverable charge capacity; a plurality of temperature sensors that sense temperature for each battery cell; a plurality of voltage sensors that measure voltage for each battery cell; the battery pack electrically connected to a battery management and control module; at least one switch to control operation of the hair dryer; a heating assembly disposed within the housing, the heating assembly including a fan attached to a motor, and at least one heating element, wherein the motor turns the fan, which draws ambient air into an inlet and expels air through an outlet; the heating element positioned such that air passing through the heating assembly may be heated to a temperature greater than the ambient air temperature; and the battery management and control module electrically connected to the at least one fan and the at least one heating element, wherein the battery management and control module adjusts an electrical current delivered from the battery pack to the fan and heating element to optimize the drying performance of the hair dryer and the performance of the battery pack; the battery management and control module including at least one microprocessor and at least one storage device; and the battery management and control module capable of measuring the temperature and the voltage of each battery cell to determine the state of charge and the health of the battery pack, and balancing the charge among the plurality of battery cells by controlling the discharge path across any of the battery cells to bleed off extra charge. a housing; a rechargeable battery pack including a plurality of lithium-ion battery cells, the rechargeable battery pack disposed within the housing; each battery cell having a discharge path; each battery cell having a beginning of life recoverable charge capacity and an in-use recoverable charge capacity; each battery cell further having a state of charge, the state of charge measured as a percentage of recoverable charge capacity; each battery cell further having a state of health, the state of health determined by comparing the in-use recoverable charge capacity to the beginning of life recoverable charge capacity; a plurality of temperature sensors that sense temperature for each battery cell; a plurality of voltage sensors that measure voltage for each battery cell; the battery pack electrically connected to a battery management and control module; at least one switch to control operation of the hair dryer; a heating assembly disposed within the housing, the heating assembly including a fan attached to a motor, and at least one heating element, wherein the motor turns the fan, which draws ambient air into an inlet and expels air through an outlet; the heating element positioned such that air passing through the heating assembly may be heated to a temperature greater than the ambient air temperature; and the battery management and control module electrically connected to the at least one fan and the at least one heating element, wherein the battery management and control module adjusts an electrical current delivered from the battery pack to the fan and heating element to optimize the drying performance of the hair dryer and the performance of the battery pack; the battery management and control module including at least one microprocessor and at least one storage device; and the battery management and control module capable of measuring the temperature and the voltage of each battery cell to determine the state of charge and the health of the battery pack, and balancing the charge among the plurality of battery cells by controlling the discharge path across any of the battery cells to bleed off extra charge.