Can I run the app without the device being plugged in?
Sure, as long as the device has battery power remaining or you are using a supplemental power source like an external battery.
If you are planning on going without power for more than a few hours, you will need to consider how you can conserve or extend battery life. We've incorporated several power management features in our Plus and Enterprise versions that can help, including the ability to dim automatically while idle on the homepage or to allow auto-lock of the screen (which requires access to the physical power button to wake).
Our Enterprise version supports going to a true sleep state, but then relies on local push notifications (based on a preset schedule) to the screen to wake. This means that when the kiosk is scheduled to wake, we begin pushing notifications to the screen and a user must perform the 'swipe to unlock' gesture to get past the lock screen, which then launches directly into the app, bypassing the Home screen.
While this means that it is possible to go to a true sleep state and recover without requiring access to the device's physical buttons (which are generally hidden by an enclosure) and that there is no way out of your content, it's not a completely self-sufficient option like our standard Night Mode, which displays a black screen, but does not allow the kiosk to go to a true sleep state. In this mode, we also dim the screen to the minimum brightness to conserve power and disable any touch gestures to the screen and can 'wake' to the homepage without any user intervention.
For projects with shorter 'power out' periods, like a simple overnight period, we've had clients who have successfully used our dimmed Night Mode, either alone or in combination with an external battery pack to help sustain battery power until the power is turned back on. As there are several variables in play, including the length of the time without power, screen brightness settings, WiFi and/or 3G usage, and the version of iPad you are using, generally some testing is required to determine whether these will work for your project.