If a dealership tells you every car battery must be replaced every three years, that’s too broad to be fully accurate. Battery life depends on climate, driving habits, the type of battery, and how the vehicle is used. Many 12-volt car batteries do start to weaken somewhere around the three- to five-year mark, which is why the advice gets repeated so often. But “replace no matter what” is not the same thing as following the actual condition of your battery.