Required when using EH-5a AC Adapter with select Nikon cameras. The EP-5B works with the EH-5d AC Adapter. The EP-5B is also compatible with the EH-5b AC Adapter and EH-5c AC Adapter. The EP-5B is required when using the AC adapter EH-5/EH-5a to power the camera. Simply insert the EP-5B into the battery chamber, powering the camera by continuous AC power instead of the EN-EL15 rechargeable battery.