The ultimate pocket tester for on-vehicle battery performance & alternator voltage testing that every service technician or gear head should have! Easy to use! Connect clips to the battery or connect to an installed SAE battery lead, then: Check battery charge level. A low battery cranks (starts engine) poorly. Start engine. OptiMate TEST records and indicates (for 20 sec) the lowest start volts. With engine running, verify charging voltage from alternator and voltage regulator.