Charging a device by placing it on a pad is convenient and measurably less efficient than using a cable. The losses are inherent to how the transfer works.
Two coils and an air gap
Power moves by inducing a current in a receiving coil from a magnetic field generated by a transmitting one. Only the field that passes through the receiver does useful work.
The rest disperses, and the proportion lost rises quickly with distance and with misalignment between the coils.
This is why a case, a slightly off-centre placement or a card between the device and the pad all reduce charging speed noticeably.
Every conversion costs something
Mains power is converted to direct current, then to a high-frequency alternating signal for the coil, then back to direct current in the device, then regulated for the battery.
Each stage is efficient individually, and the losses compound across the chain rather than staying where they occurred.
A cable connection skips two of these stages entirely, which accounts for a large part of the difference in total energy consumed.
The heat lands in the wrong place
Losses in the receiving coil occur inside the device, millimetres from the battery, and there is little room to move that heat elsewhere.
Sustained elevated temperature is one of the main drivers of lithium capacity loss, which makes heat the real cost rather than the electricity.
Charging systems respond by reducing power as temperature rises, which is why a wireless charge often slows partway through a session.
Alignment aids address the largest loss
Magnetic alignment holds the coils concentric, which removes the misalignment penalty that accounts for much of the variation between good and bad results.
Pads with multiple coils achieve something similar by activating whichever coil sits closest to the receiver.
Neither eliminates the conversion losses, so aligned wireless charging remains less efficient than a cable while being considerably better than poorly aligned wireless charging.
Where the trade is worth making
Overnight charging is a good fit, because a slow rate at low power generates little heat and the time available is ample.
Rapid top-ups before leaving are the poor case, since high power maximises both the loss and the heat while saving little time over a cable.
Treating the pad as the resting place and the cable as the fast option matches each method to the situation where its drawbacks matter least.