An engine starter motor tester applies power to a motor under test at the level normally applied while that motor is installed in a vehicle and monitors the ripple in the driving current. The ripple rate, scaled by the number of windings used in the construction of the motor, provides a direct reading of the shaft speed of the unloaded motor. This number allows a valid inference concerning the state of health of the motor, and is more certain than an estimate for an unloaded motor based on operator experience and motor “sound”. A complete test apparatus includes a stored lookup table, allowing the user to key in a product brand and model number and read directly both the RPM and the test apparatus's rating of the motor under test, expressed in terms such as percentage of life remaining.