Fist off, you shouldn't keep it on a tender all the time. When I'm not using one of my bikes I will put it on a tender every two or three days, if I am using it then, when I get back from riding and it's going into the stable for the night, I'll put it on the tender.
When you hear the clicking noise, can you tell where it is coming from, like is it under the seat or is it coming from the starter solenoid.
You might as well start by cleaning off the battery terminals and the various grounds on the bike. While I'm not sure about the XB9's, I do know that they recommend a 220 CCA battery for the 12's and, I believe most use the Big Crank batteries.
Let us know how many volts DC your getting with the battery, then start the bike and see what your getting and then rev it up to about 2500-3000 rpm and see what your getting.