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Not if done correctly. There were some early Samsung's that did it with rubber o rings on the back that helped keep the water proofing.

Not really. Expect in that obviously many of the exact current water resistant phone design can't be used. Since those don't have replaceable battery. However already at this very moment there is smart phones on the market with both replaceable battery and water resistance. Like Samsung Xcover6 pro . Not that it is the only one, but example from the major brands instead of the more niche rugged phone specialist brands. In fact in my experience in the rugged phone market replaceable battery is quite common (and thus apparently desired by customers) feature. I assume on the rugged phone user segment liking the ruggedness of "I can continue the lifespan with new battery" and even "Well I'm going to middle of no where wilderness, spare battery might not be stupid idea".

In opposite to the hurdurhurdur can't make water and dust resistant phone with battery covers. Yes we can. We figured this out by early 2000's. Touch screens on the other side of the phone taking place from the old numeric T9 pad doesn't change the design fundamentals of the back of the chassis. Rigid enough cover plate with rigid enough pressure applying latching combined with rubber seal designed and molded to seal the desired areas will do the job exactly 2027 as well as those did in 2002.

As said all it takes is a redesign job with the battery swapping idea being kept in mind from start on the chassis design. Maybe it means couple mill thicker phones, since the phone isn't a single glued together slab from front display glass to the back cover glass, so it isn't rigid by being single monolith resign block essentially. However as far as the massively bulky thick rugged phones, all phones aren't headed there. That is about impact resistance instead of water or dust resistance. Thick layers of metal and rubber both to withstand and to soften impact.

No, we have ip68 smartphone with removable battery.