A battery operating at 9V DC.

When you can power a portable project with 9V DC.

9V (pronounced nine-volt) batteries are small packages containing smaller cells connected together. Standard 9V batteries contain six Alkaline battery cells connected in series. Rechargeable 9V batteries are also available.

WARNING: You should never attempt to tear open or take apart a 9V battery; the metal is very sharp and shorting the contacts on the battery may result in injury or fire.

9V batteries have a distinctive snap-on connector. To connect the clip, align the two circular connectors with the larger circle of the clip against the smaller circle of the battery.

You can use a 9V battery clip that has bare wires (image below) or one that goes to a barrel jack. The Arduino can be powered via a 9V battery by using the barrel jack or the GND and Vin pins. If using the pins, connect the black wire (ground) to GND and the red wire (9V) to Vin.

Since this is simply a battery, it will power any program you write to the Arduino.