Patent ID: 8723526

Claim:
An internal resistance testing device, comprising: an excitation source and a battery pack, which form a loop circuit; an adjustable resistance R located in the loop circuit; the excitation source located in the loop circuit and generating an excitation voltage; a sampling unit configured to measure: the voltage between two sides of the battery pack, the voltage between two sides of the adjustable resistance R, and a value of the adjustable resistance R; and a control unit that calculates an internal resistance of the battery pack according to the voltages measured by the sampling unit and the value of the adjustable resistance R; and wherein the control unit coarsely adjusts a value of the adjustable resistance R to cause the excitation voltage to be about equal to a maximum range voltage of the sampling unit, and wherein the control unit then finely adjusts the value of the adjustable resistance R to be equal to an average value of two voltages levels recorded when the adjustable resistance R was coarsely adjusted.