What Happens Between the Pad and the Battery
The pad and device act like two parts of a transformer that are close together but not connected by a wire. Alternating current in the pad’s coil continually changes the magnetic field around it. That changing field induces an electrical current in the device’s coil; circuits inside the device then convert that current into the form its battery can store.
The gap matters. A conventional transformer has coils arranged together to transfer energy efficiently, but a charging pad must work across a case and a small air space. The coils therefore need to be close and reasonably well aligned. Shift the phone too far, or place it at an awkward angle, and less of the pad’s changing field reaches the receiving coil.
Why Placement and Heat Matter
Energy that fails to reach the device is not simply lost without a trace. Some is dissipated as heat in the coils and surrounding electronics. The phone and pad can also warm as they handle the transferred power. Charging systems monitor conditions and adjust or stop transfer when needed, but heat remains one reason wireless charging can be less efficient than using a cable.
A cable makes a direct electrical connection, so it can deliver power without relying on coils coupling across a gap. Wireless charging trades that direct path for convenience: set the device down, and power can flow without plugging in. The practical payoff—and limitation—is visible on the nightstand: a phone must stay over the pad’s active area while it charges.
