You need to power the Arduino from a battery? This changer is the perfect choice. Can even from even a single aa battery to create 5V for Your application.
Input voltage: 0.9 V - 5V
Efficiency: 96% (max)
Output port: USB
Voltage indicator: LED
When the input voltage is 1.5 V, output max 300mA
When the input voltage is 3V, output max: 600mA
Dimensions: 34 x 15 x 7