I had a Sony Xperia Z3 which had its charging port and sim tray covered by small pieces attached to the case that had rubber on them so you could open it and use the port and then seal it again. It also had a magnetic charging port that didn’t need water protection.
But iirc, it was said that the waterproof rating was only true as long as you didn’t use these pieces^^
I can think of a design where the battery just sits tight against the top part of the smartphone and you could remove the bottom part with 2 screws (whichs holes aren’t open to the inside of the phone) to spring it out like an SD-Card. That bottom part would just need to have rubber on the inside edges
Return to it and have my knowledge of all the positive and negative aspects erased would be something I’d consider. But having used all the technology for so long, I couldn’t imagine just don’t having it anymore tomorrow