Just talking about the battery/spare part issue. The FP4 battery was unavailable a few times now:
April 22
Dec 23
It became available after a few weeks back then, so hang in there and put yourself on the notification list. I also need a replacement battery, but fortunately mine is still working reasonably well.
Edit: And I think a lot of FP4s are now getting to the age where they need new batteries, so maybe there’s currently also more demand than usual.