PThomann: Using a digital or multimeter: check your wires for continuity (no internal breaks). The center of the barrel plug that fits into the camera is positive, and this wire will connect to the positive post of the battery. This wire usually has a white or grey trace line or may be dotted. The other wire is the ground or negative and connects to the negative post of the battery. If you accidently reversed these wires when connecting to the battery, it will fry a component in the camera. If this did happen, the external power supply would not work, but using internal batteries, your camera will still work.