BatteryPhone is a free utility and tools application developed by Keietsu Yasuhara for iPhone users. With BatteryPhone, you can conveniently check the battery status of both your phone and watch.

One of the main features of BatteryPhone is its compatibility with complications, allowing for automatic updates. You can set up complications using the watch app on your phone or directly on your watch. The battery status displayed in the complication is automatically updated approximately every 12 to 60 minutes, depending on the Watch OS. If the automatic update stops, simply tap the complication to restart it.

In addition, BatteryPhone provides timely notifications when the charge amount of your phone or watch falls below a specified percentage or reaches full charge. This ensures that you are always aware of the battery levels without constantly checking.

Furthermore, BatteryPhone offers a circular complication that can be assigned to the outer circle and the inner number to indicate the battery level of your phone and watch respectively. This visual representation makes it easy to quickly glance at your device's battery status.

Please note that the developer, Keietsu Yasuhara, is a Japanese developer, but the support site can be translated into various languages using the "Translate" option on the right side of the site.