Yes, apart from being flattened, heat is the biggest killer of batteries.
Being under the seat is a great advantage.
Here in Brisbane we get pretty warm summers, (though probably not compared to Arizona
) and have just had a real stinker, though much of our issue is humidity.
(Mine is 3 years old and still perfect.)
My suggestion though is to shop around when you need to replace it, don't go to your dealer unless you don't mind paying too much.