This is the DJI Mavic Battery Charging Hub.
The Mavic Intelligent Flight Battery Charging Hub is designed for use with the Mavic Intelligent Flight Battery. When used with the Mavic Battery Charger, it can charge up to four Intelligent Flight Batteries. The Intelligent Flight Batteries will be charged in sequence according to their power levels, from high to low. The advanced Charging Hub optimizes charging to improve efficiency. The advanced version charges fully in one hour less than the standard version. When used together with a Phantom 4 charger, the charging time is reduced to 2.5 hours.