This is a Canon Coupler DR-E4. It's a DC coupler (battery dummy) for Canon digital SLR cameras (such as the EOS-1D X series). It's used in conjunction with the separately sold AC adapter "AC-E4" to supply external power to the camera, enabling long shooting sessions and studio photography. It's used by being inserted into the battery compartment, providing a stable power supply without worrying about battery depletion. Compatible models: It appears to be compatible with models such as the EOS-1D X Mark III, Mark II, Mark I, EOS-1Ds Mark III, and EOS-1D Mark IV, but please confirm the actual compatibility yourself before purchasing. There are no noticeable scratches or stains, but there are some minor scratches from use. Please judge the condition based on the images, as there may be points that are not fully explained. If you are unsure, please refrain from purchasing.