Odd.
The FCC Filing (which would have been required before rolling out in the parks for any large scale testing, and indeed, was filed in October 2012) clearly shows that it is powered by a coin cell battery.
Which would imply (no, actually, require) that the units always had a battery before any wide scale public testing. The battery is for powering the active radio chip MB-R1G1 (yep, those numbers on the back of the Magicband).
I should clarify, for those unfamiliar with the terms "Active RFID" and "Passive RFID", there are some important distinctions.
Active RFID is battery operated, and requires very low signal strength with the reader station to connect. As a result, it has a very long communication range (around 100 meters or even more, given conditions). It has a much larger data capacity (128 kilobits). It is more expensive then Passive RFID per chip, but cheaper per reader (interrogator, actually).
Passive RFID has no power of it's own, as all power is supplied by the reader through short range wireless power transmission. As a result, they require high signal strength, and have a limited range (around 3 meters or less, given conditions). They have less data capacity (128 bits), but they are pretty darned cheap. However, the readers are more expensive since they are more intensive, and the readers generally will require either strong battery, or some external DC power source.
So, the Magicband has a coin cell powered Active RFID chip. This is the chip that interfaces at 2.4 Ghz with the long range xConnect xBR units (3 versions filed for those, v3.0, v3.2 and v4.0. These are the units that will interface with the Active RFID chip, and will be used to track guests, among other things.
3.0
3.2
4.0
The filing from 2012 clearly indicates that the battery is to power the radio transmitter for the active RFID functions, which is to be expected, as that's how Active RFID works. For the band, this requires FCC 15C compliance ("Low Power, Non-Licensed Transmitters").
However, the kiosk / stanchion installations use the Synapse xTP reader. It connects to the passive RFID chips in the MagicBand (there are two, one UHF and one HF, both passive as indicated in the FCC filing). The Payment pin pads use the Synapse xPD-R1G1.
Both of these readers, rather then using external antennae, have a long internal coil antenna assembly. The chips they read in the MagicBand are passive RFID, and require compliance only with FCC 15B. If they were to add a battery to the MagicBand to power these chips, then it would no longer be passive RFID, but active, and would require recertification by the FCC.
In the xTP reader, the antenna is located in the Mickey Globe.
In the xPD it is located behind the Mickey face. You can see the antenna is the green piece in the upper right hand corner of this disassembly.
The "touch" systems all use this Passive RFID system.
One more item to clear up (which has nothing to do with the original comment), but this comes up a lot. No personal information (outside of the name you chose to have printed on the outside of your band) is actually stored on the band or any of the readers.
The readers interface through a private network (hard lined ethernet, just like your home cable modem to your computer or Xbox) to servers which host the databases that house your information. The RFID chips (Active or Passive) merely have a UID (Unique Identification Number). The format, I'm not aware of, but it's probably some long string of what looks like gibberish. 6F9619FF-8B86-D011-B42D-00C04FC964FF, or something like that. Each chip will have it's own number, so you'll have 2-3 from your band.
Then that UID will be associated with your band ID. Then the band ID will be associated with your profile ID.
Anyhow, this isn't gibberish. It's the ID of the transmitter, which then associates to the band and then your profile. All on back end servers. So, it's NOT YOU. However, somewhere in the database will be a table that then connects the ID of the band to another UID which is associated with you as a person. This ID is most likely generated when you set someone up in MDE, and then when you "link" the band, you are linking the UID of your band to your UID profile.
This is actually MORE secure then you would imagine. The ability to "unlink" the media (be it the band or a plastic KTTW card) is an excellent design feature.
Anyhow, the point is, people can't get your information off the band. It's not on the band. At the absolute most (and I doubt this) they have your name stored on the band, but I doubt that...as it's really not required for the system as they have it set up.
So, there ya go. More then you ever wanted to know.