All of these replies sound way too short for battery life.
My wife's Metropolitan seems to go through a battery somewhat closer to an average of around 6 years. She's had that scooter since 2004 and I just put the current battery into it last year.
All my bikes that I have owned last around 5 years on a battery and I don't buy expensive Lithium nor high dollar AGM. I just replace the original OEM stock battery in my 2013 Burgman 650 early this year so that makes that first battery an 8 year old battery and it was really not spent, just starting to show some slight signs of age. I was about to leave on a long trip of 1700+ miles so wanted to be sure it would not die on the way. It might have made it fine, but it might not have. And I ride my Burgman, as I have all my bikes, through every month of the year including the coldest months when snow is on the ground, but NOT on the street, and temps are significantly below zero F with no issues. That's what I get for living in central Iowa.
I have had one battery in a bike show NO signs of impending failure and working perfectly... until I tried to start the bike and it was totally gone very suddenly. But usually the symptom I see is that it becomes harder to start the bike, then it will turn over but not fire until I let up on the starter and then the engine fires (has to do with the momentum of the fly wheel keeping the engine turning just long enough and amps no longer being used to spin the starter motor all allowing just enough amps to fire the plugs). That's when I know it's definitely time to get a new battery in there pronto. But like I said there was that one time when there were no symptoms and the battery was just suddenly dead.
Now I have read about a very few new batteries being DOA or dying very soon after being installed. Defective batteries. Hard to pinpoint if those are brand related or just luck of the draw. But not the norm in my experience.
A battery maintainer (NOT a trickle charger) is good to use once in a while. I don't leave one always connected when parked but I do rotate the one I have around to my bike, my wife's scooter, my JD riding mower, etc.
I also have a trickle charger that is ONLY used to attempt to recharge a totally dead battery or initially charge... which a battery maintainer such as a Battery Tender may not be able to restore or charge.