Something I came across recently when choosing a replacement battery for both my V-Strom and my KLE500.
The maintenance free batteries have the acid added and sealed in the factory before it is shipped out into the supply chain. I don't know how to tell at what date this was done. Therefore I must believe that the life of the battery has started ticking down for an unknown period before you purchase it. The battery could have already used up part of it's natural life even before your supplier has received it into his stock. Maybe this explains in part why some batteries don't seem to last as long as others.
Where as with the battery you buy in kit form where you add the acid yourself, the life of the battery will begin at this point.
Well that is how I understand how it works.