Sure. A typical pillow battery that is in your phone is bendable, gets damaged easily and is in general a fire hazard. So, to make it usable by consumers it needs to have at least some casing around it. In addition, you effectively need two back covers - one for phone internals and another for the battery. If you’ve had an older phone you know what im talking about. For durability, that’s a bit out of ass but what Ive learned from experience is that durability is not about thick cases and rubber pads, but rather, it’s all about weight - the lighter the phone is the less likely it is to crack from a fall, and all that extra bulk would likely make it more fragile.