I can't say whether or not the battery in my '06 was ever replaced, but I'm going side with it being OE.  When I first bought the bike it sat for about two months, during which time I started it up and let it idle, thinking I was doing good (but was actually discharging it).  Eventually went dead, got a trickle charger, got it charged to the point where it'd start the bike, now I haven't had any issues that I'm aware of.

I'm kind of wondering whether it's on the way out, though.  Is there any way to tell?  Don't want to get stranded.

If you ever "get stranded" you can always push start the bike.

Usually you don't change a battery if it isn't giving you any problems. They don't usually just stop working for no reason, its generally a slow noticeable decline. If replacing the battery gives you peace of mind, it may be worth it.

I guess from my experience, I knew my battery's life was coming to an end when I had to crank it a lot longer in the cold mornings.  Sometimes when the temp drops, the weak battery cannot even provide enough juice to start it.    That's when you have to get to work as well..... But generally over the course of a few days, if it takes longer to start your bike, the battery may be coming to an end.  My new battery will always turn on the bike on it's first crank, even without putting it on a tender for over a week and a relatively short commute of 15 mins at 25mph...(i know, it's so pathetically slow to ride to work in rush hour SF....) Hope this gives you an idea and sorry for the rambling, it's a thursday night/friday morning while a bit inebriated.

Why not get it load tested?

Its a free service at most places in Australia so I assume it would be the same for you.

Got your message about the Scorpion batteries and thought I'd post here to let folks know about Scorpion battery life.  I'ts been 2 years this month since I put the Scorpion in and I had to jump start it yesterday after having jump started it 2 days before but it sat for a month before that in very cold weather, was right around 32F both times.  Will see how it goes next time but I think I'll be ordering a new Scorpion soon. Riding year around here in NE Ohio I don't think I've ever got more than a couple years out of any battery, winter starting a bike is hard on batteries.  I think the better cold weather performance of the Scorpion battery and the $54 current price including shipping makes them worthwhile for me.  Didn't have to jump it the winter before and I usually do several times a winter with conventional batteries.  Walmart battery was about $35 last time I bought one and I haven't got very good life out of them, their kinda cheapos I think and look it.

My son bought a Scorpion before me and got about 2 years out of his too living nearby. About the charging issue, I just put my Scorpion in without charging it and it was OK.  Another board member here reported he had to charge his when he got it so I don't know.  They claim  "Scorpion AGM Battery ships charged and ready to install" so I'll probably just stick another one in and see how it goes.

If I bought a used bike with a battery that looked old I'd just put a new one in and go from there.  Jump starting is quick and easy since I got one of these a few years ago:

http://www.batterychargers.com/ProductDetail.aspx?ProductName=94026903

Yeah, I'm going to pick one up.  Looks like the best option, especially for $55 shipped. 

The front tire on the bike was the [dry rotted] stock, so I'm just going to go ahead and assume the battery is stock too.  Came with the cells several centimeters low on fluid and really terrible looking plates (probably maintained once if that during service life).  When the thing died I honestly thought it'd never start again, but that was two months ago and it still cranks every time.  Does seem like the bike is becoming more reluctant to start, though.  Only reason it's still going might be the fair weather we have out here.

Good info about the Scorpion battery. I have to order a new one as my current battery had to be jumped 2 times at the end of the last riding season. It's been in the garage since November....

My Scorpion battery arrived dead as a door nail but a few hours on the charger fixed it right up. It has been fine ever since.

The batterystuff order page looks like it hasn't changed since 1998 but the order went through without a problem.

I replaced my battery on my 05 last year.   It was finding if I stalled in traffic (it happens to the best of us), I only had one chance before I had little battery left for a second attempt.

My replacement battery is so much better.  Also, I put it on a trickle charger over the winter... took less than 20 minutes to get up to the green light.

Most batteries for what I've been told will last for 5 years if taken care of properly.  It's almost impossible to get a bad battery working as good as a new one.

Generally about 5 years is the end of the line.  I have a friend with an '03 bike and his battery is still good.  I have heard from folks who have had working motorcycle batteries for as much as 9-11 years although I've never experienced it.  For me 3-5 years is all she wrote.  AGM (absorbed glass mat) batteries will outlast conventional batteries whether they're sealed or have filler caps, but they cost about 50% more.