This compact, easy to use tester is ideal for quick diagnosis without having to remove wiring Simply connect the included harness to the battery in question and begin testing With the ignition off, battery voltage is displayed When the starter is engaged, cranking voltage is displayed With the engine running, charging voltage at various RPMs can be observed, indicating potential regulator and alternator trouble Easier to read than a multimeter, the Testmate is small enough to use anywhere with no need to switch between different scales