itamar224,
We recommend that you try placing the battery widget on your Home Screen: How to add and edit widgets on your iPhone - Apple Support
To perform the recommended troubleshooting steps via the link above, complete the steps in the section titled "How to add widgets to your Home Screen."
1. From the Home Screen, touch and hold a widget or an empty area until the apps jiggle.
2. Tap the Add button in the upper-left corner.
3. Select a widget, choose a widget size, then tap Add Widget.
4. Tap Done.
We recommend the steps above because they will show you how to add the battery widget to your Home Screen. That way, you can quickly tell if your Bluetooth device is connected to your iPhone because you'll be able to see the amount of battery you have remaining on that particular Bluetooth device. The remaining battery will not be displayed if your Bluetooth device is not connected.
Also, consider searching for an app via the App Store that can help accomplish precisely what you're looking for if the battery widget isn't helpful.
Please do not hesitate to reach back out to us if you have questions or need additional support.
Thanks for using the Apple Support Communities.
Cheers!