The charged currents in the outer conducting regions of the earth's core are thought to be responsible for earth's magnetism. What might be the battery' (i.e., the source of energy) to sustain these currents?

Explanation

(c) Due to very high temperature, magnetic ores in the core of Earth are in the molten state which is found to be quite good conductor of electricity. The ions in this matter, revolve along with axial rotation of Earth and thereby form large current loops which are believed to be source of geomagnetism. If this argument is correct then a planet with less angular speed of axial rotation (e.g. Venus) should have weak magnetic field, a planet with more angular speed of axial rotation (e.g. Jupiter) should have strong magnetic field and it a planet does not have molten metal in its core (e.g. Moon) should not have any magnetic field. Experimentally all of these arguments are found to be true. Hence, scientists all over the world believe that large current loops formed by the circular motions of ions in the molten state of magnetic ore in the core of Earth behave like magnetic dipoles giving rise to Geo-magnetism.
Another guessing is for circular motion of charged particles, emitted by radioactive elements in the interior part of Earth.
But still researches are going on to find out the correct reason and explanation for geo-magnetism.