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Paul Hirose you wrote:
How do you even get the batteries in? It's been a few years since I used
my A-12, but the big problem I remember was getting modern cells to fit.
Back in the 1940s they were apparently a little smaller in diameter.

Did you try alternative batteries.  My A12 came with size C zinc carbon dry cells, with ‘Sell by 1949’ printed on the side.  I now use size C Duracell alkali batteries either retail or industrial version, so I was able to compare the diameter of all three as follows:

1949 Dry cell 0.996”

2017 Duracell Retail 0.9965”

2017 Duracell Industrial 0.999”

All three fit in the containers with room to spare (see photos below).
My problem was releasing the containers from the body in the first place, and knowing just how hard to try.  They came in the end by gently twisting and pulling with a well padded Mole wrench.  I’ve lightly greased the outside of the containers now, so they come out fairly easily but leave my fingers covered in a sort of grey grease/aluminium ointment. DaveP

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