I used to be in the 'Nikon Battery Only' crowed... Until a few months ago.
I'm writing an iOS app that talks to Nikons WU-1a/b wireless controller. With the WiFi adapter plugged into the camera i can drain an EN‑EL15 in a few hours while i'm coding & testing. Rather then put lots of cycles on a $60 Nikon battery i decided to buy a few off-brand batteries.
Having put TONS of cycles (full charge to empty) on the non-nikon EN-EL15 i can say some work amazing and some are not worth the money.
I would HIGHLY recommend the 'Wasabi Power' battery from Amazon (~$24 available for 'prime'.. ships from the manufacture).
I have a few of them now and each works just as good (if not better) then the OEM Nikon.