According to this tweet, the Magic Kingdom is going to be testing charging lockers in two locations; Fantasyland and Tomorrowland. Unlike the ones at Disneyland, these will be complimentary. With smartphones being a part of MyMagic+, this will allow guests to keep their devices charged through heavy usage during their day at the park.
On 4/25, test begins w/ phone “charging lockers” in #MagicKingdom in 2 places: Fntsylnd & Tmrowlnd. Free service, phones only.
— Gary Buchanan (@Gary_Jerry) April 20, 2014