You'd be shocked - I get it!
What they need to do is put a wind generator on an electric airplane to recharge the batteries in flight.*
One really doesn't need a balloon to get the same generation, btw. A copious amount of wire as an antenna will pull elecromagnetic waves from the air and generate a current - but a very tiny one.
* Not applicable in all states. See you local jurisdiction for applicability of the laws concerning energy conservation. Designers do not recommend operating at temperatures above one degree Kelvin.