The case for this gadget slides into the back of the ICOM IC-Z1A HT and powers the radio through its usual battery contacts. I reshaped 5/16″ 4-40 brass machine screws into flat-top studs, then soldered 8-mil tin strips to their tops.
Grab a screw in a pin vise, brace it on the bench vise, and file off everything that doesn’t fit:
The result should fit neatly into the flatted recess, with the top flush in the rectangular slot:
Cut an oversized strip of 8-mil tin and solder it to the stud. I tinned both pieces to get nice solder coverage, although the notion of tinning a piece of pure tin with silver-tin solder did give me pause. It’s all in the flux, I suppose.
Anyhow, put the two tinned sides together and hit the combo with a half-second pulse at 100% duty cycle from my resistance soldering gadget. Perfect:
Then snip off whatever doesn’t fit into the slot with an ordinary (albeit shop-only) scissors, making it just slightly shorter than the slot so the end doesn’t snag on anything. File the sides and corners so they’re easy on the fingers, flatten the strip so it fits neatly into the slot, buff it up a bit, and it’s all good.
Takes longer to describe than to do it, at least the second time you do it…
The Smell of Molten Projects in the Morning 
Very neat Ed. This gives me some ideas.
I tried to make the whole contact the size of the screw head, but the radio contacts were too close to the edge of the case: I couldn’t shift the circuit board that far!
And I did try soldering using my big soldering gun and … I’m too clumsy for that.
Probably the original has the contact metal strip going through a slot in the case. Better use a lug to connect on the inside. You’ll need to plate it too, maybe a pen type plater may work here.
I wonder if you can mill a fine slot in such a situation and make the whole contact with a strip of metal.
“shop only” is good policy. Does not work here. Missing tools that I have replaced over the years have surfaced from my kids rooms and elsewhere.
the contact metal strip going through a slot in the case
Absolutely! The OEM contact strips are a fine example of industrial origami: terminals, cell interconnects, tiedowns, all in one! I suppose they’re nickel or stainless steel, with tidy welds. The slots through the case are molded and I think the strips were welded after insertion.
I pondered the situation, realized I couldn’t possibly do something like that, and went with a brass screw: round holes and flat cutouts, I can make.
The wires from the external battery do terminate in teensy ring lugs that just barely fit in the space available. You can see them there. Those wires are grossly oversized; I’ll use something smaller for the next iteration.
I’ll ignore the plating for a while and see what corrodes. If it gets wet or even damp in there, I think corrosion will be the absolute least of my worries!
Ed, where can I find 4-40 “flat-top studs”?
Nevermind. I re-read that you fashioned them yourself.