I am sure that it has been stated here already, but Disney will offer you a free RFID card just like they would in the past. These cards work almost exactly like a magic band and are waterproof. You can put them in a lanyard or a wrist holder or pocket at the waterpark.
No information is stored on the wrist band/magic band/RFID card. These only have a serial number written to them. When you scan the item a computer looks up that stored number in a database and matches it to your information.
Replaceable batteries are a difficult thing to have when you are trying to make an item small. There are only so many standard size batteries on the market and then you have to build a holder for them in the device, which takes up a lot more room than just using a tiny non standard battery that is soldered in. Look at any of the new smart phones and smart watches. Non of them have a user replaceable battery. I just want to point out that you can still use all your old magic bands at the parks. A dead battery does not stop the band from working for entry, charging, fast passes, scanning the band at say test track for the photo. About the only thing the battery was used for was long range communication like on the rides with auto pictures. Oh and the biggest use for the battery was to track you around the park. As a matter of fact the whole idea of the magic band system was to track you around the park. When this system first came out a congressman started asking questions about Disney tracking children. Igor got really really angry, in my opinion because they were caught, and said that they were not using the system for tracking. So the whole battery thing is kind of a non issue. I still use my original magic band (the old rectangular ones) sometimes they still work fine.
