The Synchros Chrome is actually the Synchros S500 in chrome-plated version. On the right ear cup, you will find two ridges. These are there to make it possible to remove the disc that covers the batteries. You just position your fingernails against the ridges, to turn the disc counter-clockwise, against a small notch resistance. The Chrome is not painted, but plated. This means that the material is now thicker, and the lid can be rather difficult to remove, because the locking notches are squeezed into position. There is no other way than to put pressure on the ridges, press downward and in a counter-clockwise direction at the same time, and press until the notches, or claws, finally let go, and the lid rotates into open position, when it will fall off. If the lid does not budge, it may be necessary to use some kind of tool, but that can damage the chrome surface. In extreme cases, it may have to go to service.