Robert

Your comment on not charging both aircraft & controller battery at the same time got my attention. So, I checked my OM for the Phantom 4 Pro. No comments on not charging simultaneously.

I googled the statement & came up with a DJI talk room discussion. Seems DJI guy says no problem with the Phantom 4 charger. Apparently the problem with some of the other DJI models is the heat the charger will make when charging multiple batteries & possibly damaging the charger. My normal DJI charger doesn't feel much above "warm". Perhaps just a little above ambient temp.

The 3 hole DJI Phantom charger works like your Mavic. Even though you put 3 batteries in the holder, it only charges one at a time. I noticed that this pretty coral blue killer charger light up both Phantom batteries at once.