If you are going to buy a 3rd party grip, a few folks had favorable remarks about these brands: Meike, Bowen (Bowers-?). And one other sold by BH Photo.
Amazon sells a bunch of types, but I for one would caution against the Pixel Vectar model. As I said, I had to return it. It would drain the camera battery in 2 days. I guess you can't condemn their customer service because they gave me a full refund, including paying for shipping. But I lost confidence with them when I shot an email to their Customer Service folks, and they were off for the two week Chinese New Year. When they returned their response to my technical question was in incomprehensible English. None of this inspired confidence.
(reading the small instruction sheet almost required a 100-power magnifying glass - it was that small)