Could power it from a jockey wheel, or a magnet in the chainring? Probably possible, but probably heavier than a wire from the main battery.
In the context of SRAM not currenlty having an electronic groupset, wireless looks like more of a USP to tempt people away from Shimano who need a reason to move away from a groupset already in it’s 3rd implementation with the bugs ironed out.
It’ll probably work flawlessly, and battery life will probably be long enough to be irelavent (think how long a cadence sensor lasts on 1 CR 2032, and that’s transmiting constantly), so the only limitation is how big a battery you can fit in the actuator, and mechs are mostly empty space or unconstrained, so probably quite a big one.