My original battery lasted about 3 1/2 years, which is pretty average for batteries in most cars these days.
Also, regarding the comment above that cold weather is hard on batteries, it is actually the hot summer weather that does the most harm to a battery. The cold requires more cranking amps, but that in itself is not harmful to the battery, it's jsut when you're more likely to need the capacity that became diminished over the summer.

 

Mine went five years and about 51,000 miles. Not 100% sure on mileage. But I was pleased.

 

my 2006 6's battery died 2 weeks ago on a hot day hear in Rhode Island. I had 43000 miles on the odometer.

 

mines dieing right now 60,000 miles.

 

My 2004 Mazda 6 Wagon (6cyl) only goes about 12-15 mos before killing a battery - but I put 36k miles a year on my car (all highway). Not sure why it goes through so many batteries, but so far have only had to pay for 1 as they all die under warranty. We clean and spray the battery terminals with anti corrosion spray every month when we get the oil changed (we put 3000 miles a month on it, so the oil gets changed every month). I have over 235,000 miles on my car, and have had to do very little work other than general maintenance. It's a peach (a battery eating peach, but still a peach!).