Gridfinity Petzl Core Battery holder 1x1

Allows charging while the batteries are in the holder.
Downside is that only two fit into a 1x1 square.

I did consider a staircase type of holder to allow access to the charging port on a 1x2 bin, allowing for 6 batteries in that bin, but I only have four batteries in rotation and didn't fancy the idea of having to remove the batteries above if I want to access the lowest one, provided the ones on top were plugged in.