That phone is a little different, you have to take the screen apart to change the battery. I had mine done at the authorized repair place and ended up having to use the insurance and get a whole new phone.
If the battery is replaced by an authorized dealer, that will ensure the warranty is valid.
The seals are beneath the battery chamber if the back is replaced correctly there "should" be no problem. Still best to ask Samsung.
Shouldnt, ask the rep though.
That's seems a question for Samsung, but inasmuch as batteries do get replaced from time to time, why would the warranty be affected? The water resistant seal/gasket shouldn't be affected when the case is opened properly to change a battery.
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