Wouldn’t it be cool if you Never Need to charge your cell phone? I’m sure that’s what many people were thinking recently, when a company called BetaVolt said it had developed a coin-sized “nuclear battery” that would last for 50 years. Is it real? Yes it is. Will you be able to buy one of these forever phones anytime soon? Probably not, unfortunately, because — well, physics. Let’s see why.

All batteries do the same thing: they generate electricity to do some kind of work. But energy is not free. If that job is blasting music on your Bluetooth speaker, there should be something to reduce the energy. In a good old AA, a chemical reaction takes place to produce the current. This chemical reaction doesn’t last forever, so the battery will eventually die.

In a nuclear battery, the power source is a piece of radioactive material, and it will run like an energizer rabbit until the source is no longer radioactive—which isn’t forever, but it’s a lot longer. These are actually not new. The Voyager 1 space probe, launched in 1977, has a nuclear battery. It’s now more than 15 billion miles away, and still has quite a bit of juice in it. That’s great mileage!

The specific type on Voyager is called a radioisotope thermoelectric generator, which is a large chunk of plutonium in a canister. As plutonium decays, it converts mass into energy, producing heat. If you put a solid-state device on it, the temperature difference between the hot and cold metals creates a voltage and causes an electric current to flow.

It’s kind of crazy that just a temperature difference can generate electricity, but you can. Test it at home. Using some copper wire and a paper clip (without plutonium), stick one end in ice water and the other in hot water. This type of power source is great for space probes because it has no moving parts, so it won’t break, and it lasts for decades.

Now, this new battery Announced by BetaVolt Uses a different technology called betavoltaic generation. Instead of tapping thermal energy, it creates an electrical circuit by capturing the emitted electrons, called beta particles, from a radioactive isotope of nickel. It is made of several layers of nickel sandwiched between diamond plates, which act as a semiconductor. There’s a lot of cool stuff to go over here, so let’s jump in.

What happens in radioactive decay?

Nickel-63 is an isotope of the stable version of the element, nickel-58. This number is the atomic weight – the total number of protons and neutrons in the atom’s nucleus. Nickel-63 has five extra neutrons, making it unstable. Over time, one of these extra neutrons will become a proton and produce a new electron. With an extra proton, the atom would now be copper 63, the next element in the periodic table. This nuclear reaction produces energy, rapidly ejecting electrons from the atom.

It is important to know that the rate of radioactive decay is not constant. It depends on the number of atoms of the material present, so the electron yield decreases exponentially with time. In the case of nickel-63, half the atoms will be destroyed in about 96 years—we say its “half-life” is 96 years.