Betavoltaic batteries are devices which creates electricity from beta radiation of a radioactive material. Alphavoltaics operate similarly, using alpha radiation. The concept was invented roughly 50 years ago and they are safe enough to be used, for example, in pacemakers.
However, the Wikipedia article on them states that they were "phased out as cheaper lithium-ion batteries were developed." I feel, though, that lithium ion batteries are hardly up to the task that consumers would want them to perform: for instance, iPhones hold their charge for about a day and notebooks can sometimes manage no more than four hours. Betavoltaics, on the other hand, can hold their charge for years.
Why, then, are they not used in commercial applications? What are their relative advantages and disadvantages with respect to the current solutions, and in particular to lithium ion batteries?
Amount of electricity is tied with half-life. For example, if Ni-63 has half-life of 100 years this means, that mole of Nickel will produce Avogadro/2 electrons during that 100 years. This means 10^21 electrons per year and 10^14 electrons per second.
This means up to 0.1 mA or electric current.
The energy of electrons from Nickel is 67 keV. This means that each electron has 67 kilovolts of electric tension.
So, the power of electricity from one mole of Nickel-63 is 67000*0.0001 = up to 6 watts.
Other way to calculate. If Nickel-64 produces 10^14 electrons per second, each of 67 keV of energy, then the power is 7 * 10^4 * 10^14 ev/s = 7 * 10^4 * 10^14 * 10^(-19) = 0.7 Watts.
So, the numbers are consistent to the order of magnitude.
Approximating, one mole of Nickel-63 provides 1 watt of electricity approx.
This looks sufficient for many cases including iPhone power consumption.
1 mole of Nickel-63 weights 63 grams. iPhones accumulator can weight more than 100.
So atomic batteries can supersede conventional batteries, and serve for years.
So why we don't use them?