As squirrel said, what you are experiencing is a cell in the battery starting to die. Most vehicles have extra capacity relative to their needs on the battery, so a user doesn't notice it at first. With the big jugs on a Ducati and the smallest battery they thought they could get away with, you see it sooner.
What often happens is a layer of sulfate crystals (sulfuric acid in the battery remember) forms on the surface of the plates. This is an insulator and makes it difficult for that cell to not only discharge, but also recharge normally. It becomes weaker and weaker with normal charging voltage. This also accelerates sulphation of that cell, a positive feedback loop. Some chargers have a "desulphation" cycle that hits the battery with extra high voltage to attempt to "break through" this sulphation layer, but that only delays the inevitable. Once a cell becomes unbalanced with the other five, it will be the one to fail almost every time.
99% sure a new battery will fix this. If the charge voltage is up around 14.0V at 2000 rpm, knock that up to 99.99%.
What often happens is a layer of sulfate crystals (sulfuric acid in the battery remember) forms on the surface of the plates. This is an insulator and makes it difficult for that cell to not only discharge, but also recharge normally. It becomes weaker and weaker with normal charging voltage. This also accelerates sulphation of that cell, a positive feedback loop. Some chargers have a "desulphation" cycle that hits the battery with extra high voltage to attempt to "break through" this sulphation layer, but that only delays the inevitable. Once a cell becomes unbalanced with the other five, it will be the one to fail almost every time.
99% sure a new battery will fix this. If the charge voltage is up around 14.0V at 2000 rpm, knock that up to 99.99%.
