Battery Widget Question

Hi,

I'm using the battery widget on my iPhone. I can easily see that current battery level of the phone and my Apple watch. I'm also using Sony Bluetooth headphones which the battery widget also displays. Question is: is the widget actually capable of measuring the battery level of the headphones? I've been using the headphones for about 2.5 hours a day for the last 3 days and the battery level according to the widget is full. Or is the widget not capable of measuring the actual battery level and just shows the full battery level for 'cosmetic' purposes?

Thanks