Nikon recently has registered the MB-N10 battery pack for Nikon Z-mount full frame mirrorless cameras in Korean Communications Commission. The MB-N10 battery pack will be the first official battery grip for Nikon Z-mount mirrorless cameras. Expect announcement for this battery pack along with Nikon Z9.
From Korean CC:
“An KCC / MSIP RR ID is the authorization ID assigned by the Korean Communications Commission to identify wireless products in the Korean market. The RR assigns application ID numbers and Authorization number to approved products. The Battery Pack, manufactured by Nikon Corporation and sold by Nikon Imaging Korea Co., Ltd. has an Authorization Number of RR-NKR-MB-N10 and was approved on 2019-06-25 under application number 201917210000159850.”