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New EU regulations mandate user-replaceable batteries in iPhones
(appleinsider.com)
This is a most excellent place for technology news and articles.
How can it stay fully waterproof?
Water resistant: By being negligibly more expensive to properly engineer and build
Fully Waterproof: By being a fair bit more expensive to properly engineer and build
In both cases, the cost is reasonably tiny, compared to the markup of the price on the actual cost
Yes but how do you properly seal the phone without stuck components?
Gaskets, yes. See any wrist watch (except smartwatch) serviced or battery replaced. Very sensitive things that claim water resistance.