The NFC chips in magic bands basically work forever they don't require power.
I generally use my phone to open the door however the last trip half way thru my vacation all of our phones stopped being able to open the door. Absolutely no one at the resort had any
clue how to fix it or even try to fix it. One of the managers actually said with a straight face maybe it got demagnetized, my phone demagnetized.......ummmmm ok???? At that point I knew it was a lost cause. There solution was to give me a key card which I took however a day later the key card stopped working. The one thing that worked absolutely flawless the entire time was my son's magic band which we used the rest of the trip just to get in the hotel room. My phone and apple watch worked awesome for park entry and
lightning lane the entire time. This is probably one of those once in a lifetime issues but just be aware it can happen so I would bring a magic band with you even if it's just the puck and not the entire band.