The sensors are not designed to have the batteries replaced. That's not to say that the sensors can't be opened up to replace the batteries, they can be. No dealer is going to do it that way though. They'll want to replace the entire sensor, the way Kawi designed it.
As for there being three different parts? I'm pretty sure that the last part number has superceded the others. No one seems to know what the differences are between the three though.
If your bike is still under warranty, this will be covered by Kawi.