The battery is in your trunk, under the black tray on the right side.  Your
owner's manual clearly shows how to access it.

Tom K.

The battery lives in a hole behind (more towards the rear of the car) the
Right Rear tire. From inside the trunk, lift the carpet from below the right
brake light, the battery lives under the cover you just exposed by lifting
the carpet. If you continue to pull the carpet aside, you will find the
spare tire living under a cover in the center of the trunk. If you've ever
found the spare before, find it again, and look to the right ...

The alarm is not connected directly to the battery, it is connected to the
fuse block, which is then connected to the battery. Knowing where the
battery is will not help you very much, except you could disconnect it in
order to get the alarm to stop blaring. The problem with this tactic is that
you will lose many other settings that your car has stored -- travel
distance for the Auto Up feature of the windows, the radio stations you have
programmed, memory settings for the seats, those sorts of things. And, odds
are that the alarm will remember that it was on the last time there was
power, and it will come on again when the power comes back.