I just had a similar issue on my 2012 M796 that I bought new in 2012 and had the tender connected whenever I am not riding. I could only ride once or twice a month and the bike has about 4600 mi on the original battery.
It started last December where I would turn on the ignition, everything appeared fine, but when pressing the starter button, I heard the click, engine did not turn over, and then the "000005 rsw" on the dash. The bike would eventually start after off and then on the ignition a couple of times. Once it started, I could ride 70 miles with a couple of stops of no more than 2 hrs and the bike would start fine.
This happened twice in December 2017, after the bike was parked for about a week. After doing some research online, I checked the battery and the voltage readings appeared to be within the spec during power on, starting, and idling. So, I called my Mechanic (Scott Waters at Motoservizio, Signal Hill, CA) and he told me with the condition of my bike, it is most likely the battery is getting old. I then took the battery to Cycle Gears and they confirmed that the battery is ok, but they do not have a load tester. Bought a new OEM Yuasa, since they had it in stock, put the acid in, waited 20 min, slow charged it for 8 hrs, and have not seen the issue back for the past couple of rides this month. Again, the battery is on Tender when parked at home.
On a side note, I have Scott did the valve adjustment and changed the timing belts at about 4,500 mi, since I was concerned about the 5-year old belts condition. He actually told me to just do this at 7,500 mi, but he did agree that I should at least have someone check the belts at least once every year. I decided to just replace them and when I went picked up the bike, he showed me the belts and they are still in good condition with no cracks. He did mentioned that one of the vales was a bit tight, though.