About how often do you have to change your car battery from new to used up?

Batteries can last as little as 1 year to as long as 7 years and up. All depends on the quality of the battery and climate. Extremely hot or extremely cold conditions put extra strain on a battery. Run the battery down and you take years off it's life. Run it down 2 or 3 times and it will fail at any moment. So there is no real answer as to when to change your battery. In my experience 5 years is about average.