I forgot to buy batteries for my new split keyboard. Is there any good place to buy the 301230 3.7v 110mah battery, to get it within a week in Norway, or is it expensive to not buy it from China with 30 day shipping? If it is not possible to buy it: Are there any other good replacements which are compatible with the nice!nano and Ferris Sweep?

I made a mistake while ordering the parts for the Ferris Sweep: I only ordered one 301230 battery. I ordered the other one, but the >1 month delivery time is a bit long. I am wondering if it is possible to solder and build the keyboard now, while only installing battery in one of the sides, and use the only side only with USB-C. If yes, I have two more questions:

1. Which side should I install the battery in? From my understanding, one of the sides usually works as a "hub" for the other side
2. Is it easy to add the battery to a already assembled keyboard in the future?
3. Are there any good tutorials for assembling the wireless variant of the Ferris Sweep? I have mostly been able to find resources for the wired versions.