A standard AAA battery can deflect a compass needle and cause it to point in the wrong direction.

The Earth's magnetic field is surprisingly weak, measuring between 25 to 65 microteslas at the surface. In contrast, even small household items like a AAA battery contain ferromagnetic materials such as steel that can distort local magnetic lines of force. This phenomenon is known as magnetic deviation, which occurs when local objects interfere with the Earth's natural magnetism.A study by the British Geological Survey highlights that magnetic interference can be caused by both 'hard iron' and 'soft iron' effects. Hard iron interference comes from objects that have their own permanent magnetic field, while soft iron interference comes from materials that become magnetized when placed in an external field. A AAA battery typically features a nickel-plated steel jacket that acts as a soft iron distorter, pulling the compass needle toward its mass.Furthermore, if the battery is part of an active circuit, the flow of electrons creates an electromagnetic field according to Ampère's Law. This law, formulated by André-Marie Ampère in the 1820s, states that an electric current produces a magnetic field proportional to the current's intensity. Even the small current in a low-voltage device can produce enough of a field to render a handheld compass inaccurate within a few inches.Professional navigators and organizations like the U.S. Geological Survey (USGS) recommend keeping compasses at least 4 to 6 inches away from small metal objects and up to several feet away from larger electronics. This ensures that the needle responds only to the Earth's magnetosphere rather than local magnetic 'noise.' Understanding these local variations is critical for accurate orienteering and wilderness survival.