How often does a car battery need to be changed?

roughly every 3 to 3.5 years. 3 yeasr give's maximum battery power. check your dealership for the most optimum battery to use and maintain

wrong,replace a battery when it dies,wont hold a charge.most batterys today last at least 7 years or longer.

While Jonathon is correct about power output, it is not necessary to replace your battery every 3 years. A good rule of thumb is to begin monitoring the health of your battery after 5 years, with the expectation of replacing it around year 7 or 8.

When it's dead.

Thanks for all the answers about the battery, my new battery in this mustange was replaced last spring, and I bought the car new in Spring of 2006 (it was 5 yrs old but I would leave the dome lights on sometimes and didn't drive it much since it's owner, my daughter, moved to NYC in Summer of 08), so I'm thinking it was from lack of use and my leaving the light on that brought on an unstable and unrelieable battery...It was almost dead, I think. Even my Murano never had a battery last 7 yrs...It's on it's 3rd one at age 8yrs...

i bought a new 2004 mazda6 and i never changed it or never had any problems.. now i just trade it in for a toyota.. i would say until it dies

battery life is around 4 to 6 six years

The NRMA are saying I should replace my battery as it has been 4 years but I see none of the symptoms which would lead me to do so. If I do start seeing the symptoms then I will look at changing it. On the next service I will have my mechanic check over it anyway to see if it is on its way out.