I was told through the "grapevine" batteries only last 5 years. Mine went a full 7 but the car only had 63k miles on it. When mine went, my headlights started to blink on and off when the car was ideling parked. No other problems starting/running...seemed to be going strong...just that darned blinkety blink. Once the new battery was installed, no more blinkety blink.
Make sure you buy the specified battery for our year 2000+ ....being placed under the rear seat, you have to buy the more expensive batteries with the side vents to let out the gases.
Around here, they were priced out for $120 retail... I got one through a relative who works at a car parts place...$80.