Almost nothing to be honest. I just added a battery percentage display to the other info I show when starting a new terminal and it worked out of the box. Same for architecture which I added to make sure I knew if I was in an arm64 terminal or a x86_64 one run through Rosetta. On the G4 it happily reports "Power Macintosh."
I have had a few issues I can't recall off the top of my head just down to really old versions of stuff. There's always "the old way" to do something and it can be fun to figure out.