From Stepper Motor Quickstart Guide - SparkFun Electronics:

Stepper motors require more power than can be supplied by the Arduino. In this example we will be powering the Uno with a 12V external supply. Notice that the power input (M+) on the EasyDriver is attached to the Vin pin on the Arduino. This will allow you to power both the Arduino and the motor with the same power supply.


12V Power To properly power the stepper motor, you need at least 12V. A USB battery pack typically is only 5V and will not provide enough juice to push the weight of a camera (be it a lightweight GoPro or Mobile Phone). I highly suggest using either a 12V power wall adapter or 12V battery pack. Wall Adapter I mostly use the camera slider indoors. Having it plugged into the wall is nice because I don’t have to worry about batteries getting low and dying. This 12V DC 1000mA power adapter works great with this project.

The Arduino Uno has a barrel jack power input, and can pass through 12V power to the driver board, so I think this is the best way to go. I have several old 12V wall-warts that can supply 1-2 A of current.

For portable power, an 8 x AA battery power pack is probably the best option.