The nine-volt battery, or 9-volt battery, in its most common form, was introduced for the early transistor radios. It has a rectangular prism shape with rounded edges and a polarized snap connector at the top. This type is commonly used in walkie talkies, clocks and smoke detectors.
Students also use this for projects such as robotics such as remote control car, boat and other Arduino battery requirements.
The battery has both terminals in a snap connector on one end. The smaller circular (male) terminal is positive, and the larger hexagonal or octagonal (female) terminal is the negative contact. The connectors on the battery are the same as on the connector itself; the smaller one connects to the larger one and vice versa.
Connectors are sold separately.
This is not a rechargeable battery.
Other types of batteries, chargers, connectors are also available.