Nuclear batteries run off of the continuous radioactive decay of certain elements. These incredibly long-lasting batteries are still in the theoretical and developmental stage of existence, but they promise to provide clean, safe, almost endless energy. They have been designed for personal use as well as for civil engineering, aeronautics, and medical treatments.
The almost magical production of electricity in nuclear batteries is made possible by the process of betavoltaics. Through this technology, the electrons that radioactive isotopes regularly lose due to decay can be harnessed and directed into a stream of electricity. A semiconductor, possibly made from silicon, catches the flying electrons and directs them into a steady power source. Even a small amount of radioactive material will provide a charge for a very long time before it expires.
Some people want to develop nuclear batteries to solve the pesky problem of your cell phone running out of juice just as you were writing down an important address. But other researchers see the potential for nuclear batteries to power things in situations where a battery really needs to last a long time because there is no way to replace it. They suggest applications such as pacemakers or other implants, detectors to be dropped in the bottom of an ocean or sealed deep within a bridge. Perhaps interstellar flights could be powered by a series of batteries each lasting several decades.
Don't let yourself be put off by the name "nuclear" batteries. You would not be coming in contact with a miniaturized nuclear reactor. In fact, once engineered to everyone's satisfaction, they could be much safer than ordinary chemical batteries. The radioactive elements are fairly rare, distributed as they are across a semiconductor, and would be very well insulated. Unlike alkaline batteries, these wouldn't corrode.
Scientists are still working out the kinks in nuclear batteries before they can be widely implemented. Of course, they have long theorized that radioactive decay could provide a low-cost source of energy, but there are many problems with getting a current that is strong and dependable enough. One of the latest developments is to use silicon wafers with a large surface area, accomplished with texturing that puts pits and valleys across the thin semiconductor. This seems to boost the usable electrical output, as it catches more electrons rather than letting the radioactive isotope re-absorb them.