Cute idea, but physics says it’s not nearly as powerful as they claim. C14 decays pretty slowly (5700+ year half-life) so even if they captured 100% of the energy, it would take 2365 pounds of C14 to generate 1 kW of power. Even the most conservative driver needs substantially more.
it could work for tiny power draws, like a watch battery. But, by the time you get up to cell phone battery demands, it’ll take a pound of C14. Account for less than 100% efficiency and the other battery materials (anode, wiring, packaging) and I’d be amazed if the phone comes out under 20 pounds.