I wouldn't worry about getting a "genuine Nikon battery"

I've owned over a dozen cameras and many more other devices, phones, GPSs, etc that took addon batteries over the years. I have NEVER ONCE bought an OEM battery for them, I just buy 2 for $9 cheapies off eBay and I've never had any trouble at all. In some cases the knockoff batteries have outlasted the OEM battery that the camera came with.

Sometimes they're as good, sometimes only 90% as good, but typically they're 20% the price and I don't usually care that much whether the battery in my digital camera lasts 5 weeks or 5 weeks and 3 days before charging.