The lifespan of a car's 12V battery can vary. Just to be safe, you could have it replaced every 2 to 3 years. This is especially the case if you're using your car a lot, or if your car regularly draws plenty of electricity. For example, cars that have an abundance of in-car electronics and other electrical components will force the battery to work harder. Thus, stressing it out and prematurely wearing it. However, some other estimates say that the aforementioned figures are too early. They claim that a battery is easily able to last between 4 to 5 years. A general rule of thumb would be to replace it every 4 years. But, also bear in mind the numerous symptoms that might indicate a weak battery, and have it replaced accordingly.