A Chinese company has unveiled a battery smaller than a coin that its makers say can generate steady electricity for fifty years without ever needing to be charged or replaced. The device, called the BV100, comes from Beijing-based Betavolt New Energy Technology and works by harnessing the natural decay of a radioactive isotope rather than storing chemical energy the way conventional batteries do. While the BV100 itself produces only a tiny amount of power, its underlying technology points toward a much bigger idea, betavoltaic batteries capable of powering small devices reliably for years or even decades at a stretch, addressing…