Granted, some replicas are cheaper. But is cheaper and cheaper? I now have the 2 original battery, they operate reliably and perfectly (with my D7000). Trigger counter, capacitance, etc., are as it should be. I (and many others) have spent a lot of money for a super camera, why should I save the "power plant" that drives the whole thing?
I would always buy the original battery ...
Addendum 13.5 .: the 1 original battery (1/2 year old) I have at a Tuscan trip with my D7000 in 4 days 615 photos (all in NEF format) made about 50% with an Image Stabilizer lens , about 10% with an internal flash. After these 615 photos of the battery was full even to 55% !!!