An example electrical drain test device includes a battery interface system having electrical cables to connect in-line with a negative battery post of a battery and an electrical system under test without losing connectivity to test the electrical system under test without having to reset test or vehicle modules. The example electrical drain test device also includes a battery disconnect switch. The battery disconnect switch in a first position provides continuous electrical current between the battery and the electrical system. The battery disconnect switch in a second position electrically connects the electrical system under test to the battery through a test circuit to test the electrical system under test for parasitic drain. After an initial connection, the system under test remains in electrical connection with the battery regardless of switch position.