Knowing when a car battery replacement is called for can not only keep your car on the road, but also save you the time and money of having it towed and serviced after the fact. Most car batteries are rated to last approximately five years. Absolute values on how long they are effective vary, as battery tests can only show the condition of the battery at the exact moment of the test, and not the entire chemical composition and its state of decay. It is safe to say, however, that after five years you should have your battery checked regularly to know when a car battery replacement is necessary. Signs that you may need a car battery replacement include the battery light illuminating on the dashboard, electrical systems like air conditioning, radio or headlights performing poorly, or your car not starting at all. If there are any indications that your battery is starting to have problems, it is a good idea to have it immediately checked. When a battery fails, it is typically within moments and it is permanent – so knowing about a battery problem before a catastrophic failure can help ensure your car is promptly serviced.