Below the seat cover
Take the seat off- your battery is towards the front of that compartment (near the gas tank), right under that pack of wires. You'll be able to see the contacts on either side of the wires and vacuum hoses.
The battery is located in the trunk in the spare tire compartment.
In the front rack compartment
ON 2007 KAWASAKI WAVERUNNER WHERE IS THE BATTERY LOCATED? I TOOK THE SEATS OFF AND CAN'T FIND IT AND I DON'T HAVE AN OWNERS MANUAL.
if you don't know how to work on it you shouldn't own it
In the trunk, passenger's side, underneath the trunk lid - in it's own compartment.
In the Underhood Fuseblock located in the Engine Compartment, just beside the Battery...
The Kawasaki part number is 16097-0004
== ==
My absolute least favorite vehicle to work on... but I'm fortunate enough to not have had to in a while. In front of the driver seat, there's a compartment in the floor. That's where your battery is. I don't remember offhand how it's strapped inside the compartment, but it should be pretty self explanatory once you see it.
The fuse panel is under the dash panel on the drivers side , and the power distribution box is in the engine compartment ( Ford states before servicing anything in the PD BOX in the engine compartment to disconnect the battery )