A 9V battery is a common, rectangular-shaped power source used in various electronic devices, such as smoke detectors, remote controls, and musical instruments. It provides a 9-volt output, making it suitable for low-power applications. The battery typically consists of six smaller cells connected in series to produce the required voltage. 9V batteries are known for their compact size, making them easy to integrate into portable devices. They are widely available and often used in both consumer and professional electronics.