TopDiag BT400 4in1 Battery Tester For OBD 2 Car Truck Battery Analyzer Tester Diagnostic Tools Battery Monitor With Software. TopDiag BT400 4in1 functions：. Prepare an extra spare vehicle battery, Connect the device to the spare battery correctly with red clip to positive black clip to negative pole, Plug OBD2 adapter to thData Link Connector socket in the Vehicle.