Perpetual motion machine?
No, they say it takes heat to recharge the thing. That's where the energy comes from.
But, it does sound at lest potentially promising as a storage mechanism, and portable, rechargeable source. Provided it holds more and weighs less than batteries.
Usefulness also would depend on the efficiency of the conversion of the heat to the stored energy.
But wait. There's more! (energy, that is)
Cheers!