When I first started hunting around for a bike, back in the Spring 2010, I also found a 2006 model. The guy had let it sit in his garage over the last year, and it had really low miles.
He brought it around the alley from the back of the house, to the front street, where I was, with no delay. Shut it off, I looked it over, and took it for a spin.
Brought it back to the front of the house, we talked for a bit, but he wouldn't budge on his price, which was a bit too high. Told him that I'd have to think about it, and we'd get back in touch.
He went to start the bike, to take it back around to the garage in the rear alley, and it wouldn't start. I didn't end up buying the bike, but mostly due to the price, not the battery or the bike not starting.
My gut-impression from your story, and with information you've NOT clearly provided, is that this is the Original OEM battery, and it's five+ damn years old... All you said is that the owner "charged" the battery!?
Just go to the store, get a new battery, and you'll be fine! It's a HONDA!!!!