I bought a Pearstone for my DiH a couple years ago when the original EN4 finally died. It's still fine. I have been looking for another but I don't think they make it anymore. The D1 I just received had a Calumet EN4. I see Calumet still has it in stock for about half the price of the Nikon.
I have a Power2000 spare battery for my D800 but I didn't see any EN4's in stock anywhere.