How an iPhone wireless charger works.

The majority of phones capable of wireless charging use what’s called the Qi format — its a standard method of transferring power that uses a charging base. It’s important to remember the Qi designation when looking for an iPhone wireless charger.

Wireless charging technology relies on sets of electromagnetic coils. There’s a transmitter coil located in the charger itself, which creates an electromagnetic field with the coil located inside a phone. This method, called inductive charging, allows a battery to be charged without being directly connected to the power source.

However, the size of the coils is important. Larger coils are capable of more powerful outputs, which means the charger and the charged device can be further away from each other while still maintaining an electromagnetic field. With smaller coils, such as the ones found in a mobile phone wireless charger, the two coils need to be pretty close to each other to power the battery. A fast charging charger will be 10w whereas a normal charger is rated at 5w.