The Atomic Battery is a type of Battery that is able to produce infinite power, but has a lower output than that of a normal battery.
Atomic Batteries can be used to generate power indefinitely.
An Atomic Battery is a long-lasting, low power device. It can power one simple machine or two low-powered machines (if used with an Energy Storage Module). It does not generate enough power to keep machines with a large power demand operational - for example Electric Furnace and Refinery.
In Hard Mode most Galacticraft machines draw more power than they do in standard mode, so there will be not so many machines that the Atomic Battery will be able to operate. But even in Hard Mode it should still be useful for its intended uses in remote Launch Controllers and Short Range Telepads.
Its power output is described as "Low". After some testings, it seems that the output of this battery is about 115 gJ/s, or 5,75 gJ/t. One would need 13 atomic batteries to sustainably power an electric compressor (which is what is used for the test)
In real life, a Thermionic Battery (or Atomic Battery) is an electrical power source with extremely long life - 20 years or much longer. For its energy source it uses a radioactive compound (made in a laboratory or in a nuclear reactor) - the Radioisotope Core - which, over time, slowly decays, emitting radiation and heat. The radiation and heat is turned into electricity by the battery. The radioactive core is surrounded by lead or other radiation shielding materials so that it is not dangerous to people, so long as the battery is not cracked or broken.
These types of batteries are used where a long-lasting, reliable power source is needed in a remote location - for example some space probes and satellites have them, and also, back on Earth, some lighthouses and navigation buoys.