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While testing some vintage Futaba Magnum and Megatech Jr transmitters, I noticed that the batteries and battery holders were very tight. Like separating the transmitter handle tight.

After doing a little research, I found that AA batteries are supposed to be 13.5mm but can be up to 14.5mm. Just about every battery that I had (7 brands) were in the 14-14.3mm area, with several being 14.2mm. Only the cheap Sunbeam (Dollar Tree?) HD's came in at 13.7mm.

So if you have one of the 2PB types, pay attention with battery selection.

In the meantime, I guess I'll buy several different kinds and measure them.

I have a few different brands of AA NiCds (1000-1200mah) sitting around as my industry uses them in a standardize instrument, and they are all 14mm +/- .04.

There are whole forums and YouTube channels based on consumer battery's and a quiet battle to cram more Ah into them , I guess making the battery a little bigger is a way to do that , I've also noticed with torches and radios that it can be hard to get the little beggars out again as they are so tight , at the same time I find a lot of AA battery + terminals are too wide or not as long so they don't make propper contact .

Just an idea, but since each battery has a label, there is a seam where the two sides meet. This makes each battery a slightly elliptical form. Try rotating the cells to line up the seams along the batteries and see if this gives you the necessary half millimeter or so of wiggle room. The only other option would be to remove the labels on the cells, but that could lead to a potential short.

Final thought, if your battery tray has the raised polarity indicators pictured above, you might Dremel them down to buy you a half millimeter per row. I'm assuming you wont mix up the cell polarity at that point...

I'm thinking of getting some 1/2" plastic tubing and making some sleeves for using AAA batteries. The 1/2" tubing should be 13mm. And I'm thinking that quality AAA's should be better than cheap AA's.

I'm still working on the AAA adapters but I did find some that fit.

Went by Dollar Tree and bought some cheap HD batteries.

The Panasonic Heavy Duty (not alkaline!) are 13.8mm

The E-Circuit Heavy Duty are 13.7mm. Looking at the display, I think that these are the same as the Sunbeam batteries.
These did fit the battery holder easily and didn't bind with the transmitter case.