I have a 2008 XKR. I had a dead battery a couple of weeks ago, but after a jump everything seemed fine. Today a trouble light came on "CATS SYSTEM FAULT". I have no idea why it went on or why it is statying on. Any ideas?

 

It's (nearly) ALWAYS the battery. Once dead, it'll be dead again in short order. You can try to save it by charging it for 24 (or more) hours with a GOOD actual battery charger of at least 10 Amps.
If the charge takes you may make it a year, but probably not.