A parasitic drain tester measuring the parasitic battery drain of a vehicle and the high current used by the vehicle starter motor, includes a current measuring circuit and a unit. The current measuring circuit includes a capacitor smoothing the current distribution within the circuit, a first interface connected to a vehicle power source being tested and the capacitor, a second interface accommodating an outside connection for communication, a first processor connected to the second interface and the capacitor, the processor communicating with the second interface and performing analysis and calculation of the data received, and a converting unit connected to the processor, converting the signal received through the first interface from a first form to a second form in order to process the signal received. The first unit is connected to the current measuring circuit, and the first unit includes a memory storing information retrieved from the current measuring circuit through the second interface, and a second processor analyzes the information received from the current measuring circuit and providing instructions to the first processor through the second interface.