PodCase is an iPhone and AirPod charging case with a built in backup battery. It keeps your iPhone and AirPods in one place and charges them with a single USB-C cable. Check it out on Kickstarter.
Great idea, but it's far too bulky. The problem you're solving is to not have to carry around the case for the AirPods, though carrying this case on your phone is likely far more taxing, and even from your own photos don't fit comfortably in pockets.