I am on KDE. When I connect a Bluetooth headphone, everything works fine but there is no indication of the device's battery level in Battery and Brightness widget or anywhere in the top panel.
I need to use upower -d to check the battery level. Is there any way for the battery percentage to be shown somewhere at the top. I couldn't find any widget too.
If not, Plasma allows you to add Battery applets/widgets and some or all can display battery %. I don’t understand why you say you didn’t find any, where did you look for?
If they are not already on the list of applets you can downlaod it using the Get Widgets button in the widgets list.
Or maybe you mean none use upower -d…