Looks like the original radio has a proper battery holder! Here’s a pic of the cell in the 207. The two ends of the cell are held compressed together by a wire. I’ll try to open that up and put in a tiny no. 377 (SR626SW) measuring about 6.5mm by 2.5mm. It’s 1.55V, and I hope that isn’t too far away from the 1.25V spec!