saw something similar a few days back, a ladies bra that does the same thing, long live wobble power :O)

It's just one of those shake to charge torches with the bulb replaced with a charge cable!

Easy... One spherical magnet and either a winding in the shape of a tube, or a doughnut, depending on who's lawyers you want a visit from!

Add a couple of discrete components to smooth the whole lot out, and tada, charger.