My 06 sits in the basement for long periods of time (6 months), under cover, with no tender, and fires right up.
You need to do some investigating.
As FM said, check the Rectifier/Regulator for proper output. It may be putting out too much voltage while running and "cooking" your battery.
It may have a shorted diode and be draining you battery slightly while sitting.
I just found this situation on my ATV. Battery was stone dead. I removed the battery, charged it fully. I disconnected the R/R harness from the machine and wired the + wire from it direct to the + on the battery. I took the - wire from the R/R and connected to the + lead on my multi-meter. The - lead of my multi-meter went to the - battery terminal. The meter was set to read DC Amps. My meter is fused @ 10A. This test revealed a full 1A draw on the battery with the R/R connected which means it is shorted internally.
You may have other things on your bike causing a parasitic draw. You can test by disconnecting the battery terminal and putting you meter in between the - battery cable and the - battery terminal. Doing so will show the total parasitic draw on you your electrical system. If it is excessive, you can remove 1 fuse at a time to pinpoint which circuit contains the draw. Once you know which circuit, you need to trace it out and test individual parts and pieces.