My eBay order arrived of
just the circuit board in three days (see post #25). I used the instructions here to program the new remote:
https://www.xoutpost.com/articles/x5...ob-bmw-x5.html
Oddly, when programming the new remote, in step 5, the doors locked on the second press of the lock button (while its unlock button was held down). Is that normal? It seems to be working now and the seat changes position depending on which I key use.
However, I misunderstood something fundamental. With the new circuit board in the old, non-working battery diamond key, the remote buttons work, but the engine will not start. If I put the old circuit board back, it does start the engine. I did some searching and figured out what I hadn't taken into account. This thread was helpful:
https://www.bimmerfest.com/threads/i...ve-coil.518505
So I guess I'm going to have to get another diamond fob. The good thing is that I have a second working remote now which was my main motivation for this project. The other original diamond key's factory battery is still working after 17.5 years. Pretty amazing!