most batteries last 4 or 5 years. sure i've had batteries that last longer. but they don't always show signs of age until they croak for good. My '02 3.0 died last year at just 4 years of age.
My point is that you can change it now under controlled circumstances or risk getting stuck. Then you have to call AAA or get a jump and you're wasting time that is probably worth way more than the little bit more use you get by keeping it.