Try t-motorsports gel-cell batteries. Had one that lasted through two TMEC 200 enduros. I let the bike sit for several months, and finally, after two or so years, corrosion got to where the wires bolt on, rendering the battery useless. I knew I should have disconnected the battery!
http://www.t-motorsports.com/batteries/?sort=priceasc
The catch is that you have to measure yours, and see if they fit within the confines of the replacement battery, which was what I did. The advantage of the gel-filled battery was that they shipped it complete, ready to go (of course, you want to put it on a trickle charger, first), since you don't have to squeeze in the acid, although they do carry acid-filled ones, too.