You are correct that the bike should be charging the battery during the ride, so is it? Perhaps your charging circuit went out and you were running the ignition and accessories off the battery during the ride. The above test is designed to check for that as well, as in "What is the voltage while running with the engine rev'd up a little bit say 3,500 rpm?". If it's not above 13.5, you may need to look at the charging circuit. I have not experienced it on this bike, but I believe the alternator (stator?) connector has been an issue for some.