Where is the Back up battery located?

Hello! My name is Branden with Silver Arrow Autohaus. Your vehicle only has the one "large" traditional battery under the hood. Your vehicle does have an alarm siren which is a kind of all in one standalone unit that has a horn, a battery and a circuit board in it. The batteries in these fail and cause issues with the alarm. More than likely whoever told you your back-up battery was bad probably meant the battery internal to the alarm siren. If you need any help diagnosing, or replacing the alarm system on your car please let me know. After replacing the alarm siren it is best to clear all related anti-theft codes from the computer modules with a proper scanner. There isn't any adjustment you can do yourself, on my end the only real "adjustment" I can do is to change how the alarm siren chimes when you lock/unlock the doors with the remote key. If there is any further information I can provide please let me know.