Well, I guess I am a heretic too. When I bought my D7000, I ordered a second battery from the vendor. It was a non Nikon, and I don't remember who made the spare battery? However, it is still working over two years later. I charge it along with the Nikon battery and run both together. One in the camera and the other in the non-Nikon grip.
In my D700, I have the same setup. I purchased it second hand and it came with a Nikon battery and a non Nikon battery. Both batteries work just fine.
I agree however, stay away from the eBay batteries. Buy a spare from a local camera shop or one of the well known big internet Camera stores.