I run a 100W Phantom 4 charger in to an Advanced hub, it’ll charge three at the same time and the fourth one begins as soon as the first of the three complete (if that makes sense). It also charges the CS batteries (albeit one at a time) and the Mavic remote too.
More info re hubs: Differences between Mavic charging hubs explained
I’ve not seen a M2 battery in the flesh, are the connectors the same as the Mavic Pro? Or maybe theres an advanced hub for the MP2?