Monitor your iPhone battery level from your wrist.
Juice Watch is a simple app designed to do two things well:
See the battery level of the paired iPhone in a complication on Apple Watch
Get a notification on your iPhone when your Apple Watch is charging and gets above 90%
Just glance at your wrist to monitor the charge of your iPhone throughout the day. Or, keep tabs on the battery level of your iPhone while it is plugged in and charging in another room.
Juice Watch is available for a wide variety of complications, so you can use it on your favorite watch faces.
You can also check your Apple Watch battery level from your paired iPhone. This can be useful while your Apple Watch is charging somewhere else.
Keep in mind that the iPhone battery level shown on the Apple Watch is not real-time. It is refreshed periodically, about every 530 minutes. The Apple Watch battery level shown on the paired iPhone refreshes at approximately the same rate.