If the battery is never allowed to go flat it can last well over 10 years. I replaced mine after 10 years after I fitted heated grips because they would switch off with the engine idling at traffic lights. The new battery made no difference.
But AGM batteries do not like going flat and being asked to deliver high currents when partially discharged. Just one occasion of carrying on trying to start an engine until the battery won't turn the engine over or the solenoid clicks can ruin a battery and it won't hold a charge properly again.
Just common sense says it would appreciate a new one after 10 years though, i don't even understand why anyone is even questioning it?
EEK -- so far - touch wood. I am on the original 17 year old battery but when I am not riding it I keet on a yam branded C-Tek charger here http://www.yamahaclothing.co.uk/yec-40-battery-charger-3227-p.asp.
I brought it a few years ago after I also had a starting issue and almost flattened the battery, my issue was the spark plugs, I had them out and they looked fine but brought some new ones anyway and hey-presto fired straight up.
May be my battery has lasted so long because I only for fun when its dry and so am not starting it up twice a day every day.
If you add up how many times my battery has started the bike compared to a bike used every day then the battery is about 4 years old
Why does that not surprise me at all?
There's loads of things to chuck into the equation with batteries and how long they last.
My bike is used for fairly short journeys most of the time, at least 5 days a week, but then it will sit outside in all weathers, including very hot or very cold weather.
Then there's the headlights, I've done the mod so they're both on, and they stay on all the time when riding.
Also I have heated grips which I use for a large part of the year, and I now have the added spotlights as well.
I do make a point of switching everything off though when starting the bike to avoid any unnecessary strain on the battery even though it would handle it if it's in good nick.
At my work we have batteries that we use for my video equipment, plus cameras as well, so I do get a rough idea about battery life, 'cos they are in constant use being hired out and charged all the time, and they are similar to bike and car batteries.
So I think 17 years (probably more actually) is a pretty good innings I'd say, and I doubt anyone else can really top that I'd imagine!