I have a couple of jetworks that are 6 years old, and couple more in the two -three year range. In fact, that's all I'll sell anymore. I have a buddy that despite being able to get dealer cost on the JW from me, still runs the Odyssey, and still replaces them every year....kinda hard headed. They also will fit the Kawi 750, as inquired in a previous post.
I had a yuasa that was used by the VA Hospital in medical equipment, they have to change them out for routine maintenence, so I have no idea how old it was when a buddy drug it out of their dumpster. Anyway, he used it for two years, traded the ski into a local dealer, I ended up buying it about six months later, rode it for a year, sold it to a guy that owned it three years prior, he had it two years. My buddy was looking for a ski, so we called him and ended up buying it back, and my buddy rode it for a couple of years, bought a new battery just because, put this old yuasa in another ski that he sold, and I know the thing lasted another year anyway. Lost track of the battery after that. They sure don't make'm like they used to..LOL!