I can't see how it would be possible to build something in the AirPods form factor with replaceable batteries. So any such device would have to be substantially

I can't see how it would be possible to build something in the AirPods form factor with replaceable batteries. So any such device would have to be substantially larger (possibly to the point where it would no longer be comfortable to wear, or to carry the charging case in a pocket). And from my experience, wired headphones tend to break after a couple of years as well, for different reasons.