Smoke detectors can use different types of batteries, but the most common ones are 9V and AA alkaline batteries. Some smoke detectors use coin cell batteries. A 10-year sealed battery smoke alarm is also available and recommended by some manufacturers. The battery in a smoke detector should be replaced every six months. Some smoke detectors use lithium batteries that can last for ten years. It is important to choose the right battery for your smoke detector to ensure it operates properly. If you are unsure which battery to choose, it is advised to pick batteries developed especially for smoke detectors and in compliance with safety standards. When changing the battery, make sure the negative and positive connections match the labels in the smoke detector. Fire safety experts recommend replacing smoke alarm batteries two times a year, and a good rule of thumb is to change them when the clocks change in the fall and spring.