The battery icon in your iPhone's status bar gives you a visual idea of how much power is left, and there's a battery percentage option you can switch to or view in the Control Center, depending on your model.

1. Open the Today View Settings
Swipe right from the home screen, lock screen, or Notification Center to access the Today View, which is where all your widgets live.  Scroll all the way down until the "Edit" button appears at the bottom, and select it.  Your iPhone must be unlocked to access the widget settings.

2.Add the Batteries Widget
Once in the Add Widgets menu, tap the green plus (+) icon next to the "Batteries" widget under More Widgets.

3.Check Your Devices' Battery Levels
The added Batteries widget will be seen on the screen where you placed it. You can see the battery percentage of bluetooth earbuds and mobile phone seperately. If you're on the lock screen or main home screen, it's just one quick swipe right.