I just bought an OEM extended battery cover for the HTC Rezound on Amazon (at least, the vendor claimed that it was OEM).
I know that some components of the Rezound's transmitters/receivers are located on the inside of the battery door, so that if you get the wrong kind of door, your phone might not have 4G or other capabilities. I'm not sure whether the door I ordered is supposed to support 4G (this was missing from the vendor's specs).
Here's a shot of the inside of the extended battery door I just bought. I would guess that it doesn't support 4G, but what do you think?
Also, if you have a Rezound extended battery, what does the inside of the cover look like?