A battery and charging system tester includes an automatically-operated carbon pile for loading the battery, the pile having a shaft therethrough rotated by a stepper motor, and a compression nut threadedly engaged with the shaft for movement into and out of engagement with the carbon pile in response to rotation of the shaft for varying the compression of the pile and, thereby, the impedance thereof. Probes are provided for sensing battery load current and output voltage, and the output current of an alternator charging unit. A feedback control circuit including a microprocessor operating under stored program control converts the analog probe outputs to digital signals and compares the battery output voltage and load current to selectively variable references for controlling the stepper motor to vary the battery load so as to regulate either the battery load current or the battery output voltage to a predetermined reference value, depending upon the test being performed. A selectively variable timer controls the time period during which the battery is loaded. A display indicates the reference values, the values of the parameters being regulated and the state of the timer.