And it has been my obvservation that the Charging system on the 800XC at least is not weak nor regulated to "just above the bikes requirements".
the other? Lousy batteries? Yes.
"Back in the day" if you were hard up you could scrounge around a junk yard and find a ten year old battery and run it for a couple more years with ease.
Now if a new battery gives you two solid years, let alone three, count yourself lucky.
pay ten times what it's worth and get half the life if your exceptionally fortunate.