2004-2005 Kawasaki STX-15F Jet Ski Factory Service Manual., Page 339Get this manual
14-24 ELECTRICAL SYSTEM Battery
3) When you do not use the watercraft for months: Give refresh charge before you store the watercraft and store it with the negative lead removedGive refresh charge once month during storage4) Battery life: If the battery will not start the engine even after several refresh charges, the battery has exceeded its useful lifeReplace it (Provided, however, the watercraft's starting system has no problem)
WARNING
Keep the battery away from sparks and open flames during charging, since the battery gives off an explosive gas mixture of hydrogen and oxygenWhen using battery charger, connect the battery to the charger before turning on the chargerThis procedure prevents sparks at the battery terminals which could ignite any battery gasesNo fire should be drawn near the battery, or no terminals should have the tightening loosenedThe electrolyte contains sulfuric acidBe careful not to have it touch your skin or eyesIf touched, wash it off with liberal amount of waterGet medial attention if severe