Depending on your use, the battery can last up to 5 days. On average, the battery lasts around 3 days. 

Your app will alert you when it detects your battery is low, and once you plug it in to charge, if your phone is nearby, the app will also alert you when it is fully charged! When plugged in to charge, the Band will display all light bars with one green bar (all bars blinking) to signal that the Band is fully charged.