| I had trouble with my battery after last winter (on a 2003 749S) when the Optimate said it was OK one day and weak the next, sometimes it would start the bike but mostly would not. Turned out to be a dodgy earth terminal on the battery where the connection between the terminal and the cable itself had corroded through. Replaced it and it has been fine since.
Not suggesting you have exact same problem, but just showing it can be something else that gives the impression that the battery has failed.
Or you could just need a new battery, because the modern gel ones are notorious for not lasting very long (that's progress for ya!) | 
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