LeapBand has a rechargeable battery that lasts up to 3-4 days depending on usage.  

To charge your LeapBand, use the included USB cable to plug into a USB port on your personal computer or a USB wall charger (not included). It will take four hours to completely charge the LeapBand.

To see the current status of the battery, use the right button to scroll to the battery meter on the device.

When the battery is very low, before the home screen appears, a low battery screen will display.