Technically, the original Gridfinity Battery Hopper design fits AAA batteries but after dropping a bunch of batteries in I found the gaps where large enough the batteries tended to just tumble out. This drop in insert lowers the supports to only allow one row of batteries and shrinks the width to prevent batteries from getting out of alignment.
I found after printing the tolerances where a little loose and with fewer batteries they could push up the insert bypassing the supports. A little CA glue to hold it in place made this “good enough” for me but I included a parameterized FreeCad file if you want to try your hand at improving it though.
The author remixed this model.