Locating the battery level Indicator

In 'Settings' on the top right you will see a battery icon with a percentage of your device’s charge.

If you hover over the battery icon with your reticle, it will display the percentage of battery life for both the iPhone and the headset.

When your headset falls below 10%, you'll get a red notification stating “Please charge your headset”. 

For information on charging best practices please refer to this article.