In the past, I have been content with buying my second battery from a third party manufacturer and paying mostly less than £20, as I am annoyed at the prices that companies charge for their own batteries. however, the last time i did this (for a Sony DSLR) the battery did not fit the camera or charger without adding a piece of card in for packing - so I ended up buying twice and having to get a proper battery anyway. So on this occasion, I was pleased that I was getting a proper Nikon battery for cheaper than most originals cost. the battery came boxed and the box had a stick NIKON hologram sticker on it to indicate an original product.
The company that sent it (POPCORN) were prompt (arrived 2 days later) and sent 2 advisory e-mails re the order, so I would be happy to deal with them again. the battery behaves exactly the same as the one that came with the camera in relation to charge times and performance. I bought this for my D5100.
Happy to recommend. My rating for 5 starts is based on the fact that I got an original battery for about £15 cheaper than I have experienced with other manufacturers.