If you have your own a/c adapter, you can plug in at electrical outlets located near the tables located on the right when you walk in to Backlot Express.
best bet is buy a portable charger and have it with you .....
If you rent one of the electric vehicles they have usb ports
There's a few I know of. Star Wars Launch bay has a couple, the ABC Commissary cafeteria, and PizzaRizzo right before Star Wars Land as well. You can also purchase at kiosks a portable charger. $30 I believe.
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