Solar BA9 Manual De Instrucciones página 9

Question: What might cause sparking at the connection to the negative or positive
terminal?
Answer: It is important that the tester clamps make a good connection to the
battery terminal (preferred) or to the battery connection hardware. Avoid connecting
to any screws that are used as part of the vehicle's battery connection. In some
circumstances, usually when connecting to such screws, an inefficient connection
is made that provides very little surface contact from the clamp to the connected
surface. In such cases, the tester's electrical pulse will try to follow the easiest path
to the battery posts. If such a situation occurs, disconnect tester immediately and
attempt to make a better connection with greater surface contact between the clamp
and the connected surface.