When you tap the enter button and activate the home screen on Band/2... tap the action button to cycle through the display options. Battery is not there, but perhaps you don't know about toggling what is displayed to the right of the time?
At any rate, from the home screen pull right, exposing the left edge of the screen. There is a battery icon there. It does not show percent, but is a graphic representation. Also shown is your HR and BT status (off or on).
For a percentage readout of battery, you can see it on your BT paired phone using Pimp My Band.