Many of Apple’s customers own a number of Apple devices such as iPhones, iPads, laptops, iWatches and AirPods, see Figure 3.
Figure 3: A selection of Apple products

Many Apple users found the efficient charging of multiple devices could be difficult. Apple aimed to solve this issue when they filed their patent for the AirPower, a wireless charger that could charge three devices at once. To achieve this the coils must be placed directly on top of one another, see Figure 4. If the coils are not aligned, the device will not charge.
Figure 4: Wireless charging

The AirPower aimed to solve this issue by stacking and offsetting the coils, see Figure 5. Stacked coils gave the AirPower the ability to charge multiple devices at once. The large charging area made it easier to align the coils.
Figure 5: Registered patent for the design of the AirPower, showing many stacked coils

During testing, Apple found that the AirPower was unsafe because the coils overheated. This led to Apple cancelling the development of the AirPower and the product was never released to the public.