Last year (2010), I decided to buy a couple of cheap ($35) Lawn and Garden batteries (think riding mower) for my Sea Doo GTI jet skis, rather than the much pricier official “jet ski” batteries, which typically sell for 2-3 times as much (see http://encorecbt.com/encoreWeb/boating/sea-doo-gti/projects/battery/index.htm).
Well the 2011 season is over and the verdict is: Great. The batteries worked just great for the 2nd year. Each week, I would put a battery charger on each battery for 2-6 hours prior to each weekend’s use of the jet skis. That said, we always had tons of cranking power and the Sea Doo’s never failed to start.
I should also mention that over the winter, about every 2 months, I put the batteries on a battery charger for a couple of days (just to be sure they didn’t go stone-cold-dead).
So, my advice is to save your money and buy Lawn and Tractor batteries for your jet skis, and stop wasting money on overpriced “jet ski batteries.” I’ll keep track of their longevity, but I expect to use the same batteries in 2012 too.