Reverse Wireless Charging On Smartphones: How It Works

Reverse wireless charging allows a compatible smartphone to share some of its battery power with another compatible device without using a charging cable. Instead of only receiving power from a charger, the smartphone can temporarily work as a wireless power source.

The feature can be useful when wireless earbuds, a smartwatch or another compatible smartphone is running low on battery and there is no suitable charger nearby. However, reverse wireless charging is mainly designed for convenience and emergency power sharing rather than replacing a normal charger.

What Is Reverse Wireless Charging?

Reverse wireless charging is a smartphone technology that allows a phone to transfer some of its stored battery power to another compatible device wirelessly.

A supported smartphone has a wireless charging coil inside its rear panel. During normal wireless charging, this coil receives electrical energy from a compatible charging pad and passes it to the phone's battery.

Reverse wireless charging works in the opposite direction. The smartphone uses energy from its own battery to power its wireless charging system, allowing another compatible device placed on its back to receive power.

Different manufacturers may give the feature different names, including wireless power sharing, battery sharing or reverse charging. The basic function is the same: the smartphone shares part of its battery power without requiring a cable between the two devices.

How Reverse Wireless Charging Works

Reverse wireless charging uses electromagnetic induction, which allows electrical energy to move between nearby coils through a magnetic field.

Inside a compatible smartphone is a wireless charging coil. When reverse wireless charging is activated, the phone sends electrical energy from its battery to this coil.

The coil creates a changing magnetic field around the back of the phone. When a compatible receiving device is placed close enough, its own charging coil detects this magnetic field and converts the transferred energy into electrical power.

That electrical power can then be used to charge the receiving device's battery.

The process can be simplified into four steps:

• The smartphone's battery supplies electrical energy.
• The phone sends the energy to its wireless charging coil.
• The coil transfers the energy through a magnetic field.
• The receiving device's coil converts the transferred energy into electrical power.

The two devices need to be positioned close together because wireless power transfer becomes less effective as the distance between their charging coils increases.

The Role Of Qi Wireless Charging

Qi (pronounced “chee” in English) is a wireless charging standard developed by the Wireless Power Consortium (WPC). It sets the rules that allow compatible devices such as smartphones and wireless charging pads to transfer electrical power without a cable.

The name Qi comes from a Chinese word commonly associated with energy or life force. In wireless charging, however, Qi refers specifically to the standard used for wireless power transfer between compatible devices.

Many smartphones, wireless earbuds and other accessories support Qi wireless charging. However, a phone that supports Qi wireless charging does not automatically support reverse wireless charging.

The difference is the direction in which power moves. During normal wireless charging, a compatible charging pad sends power to the smartphone. With reverse wireless charging, the smartphone uses its own battery to send power to another compatible device.

This means a phone needs the necessary hardware and software to transmit power. The receiving device must also support a compatible wireless charging system. Compatibility and charging capabilities can vary between smartphone models and accessories.

Key Features Of Reverse Wireless Charging

Reverse wireless charging is designed mainly for convenience. The exact features available depend on the smartphone model and its software.

Some phones allow users to turn wireless power sharing on or off from the battery or quick settings menu. A supported phone may also stop sharing power automatically when its own battery falls below a certain level.

Other factors can affect how the feature works, including:

• Power output: Smartphones can differ in how much power they can transfer to another device.
• Charging speed: The receiving device may charge more slowly than it would with a suitable wired charger.
• Device alignment: The two wireless charging coils need to be positioned correctly.
• Battery level: A phone may stop power sharing when its battery becomes too low.
• Temperature: The phone may reduce or stop charging if the device becomes too warm.
• Compatibility: The receiving device needs to support an appropriate wireless charging system.

These features are not identical across all smartphones, so users should check the specifications of their particular model.

Devices That Can Be Charged With Reverse Wireless Charging

Reverse wireless charging can be used with several types of compatible devices. The exact devices that work will depend on the wireless charging technology supported by both products.

Wireless earbuds: Many wireless earbud charging cases support wireless charging. If the case is compatible, it can be placed on the back of a supported smartphone to receive power.

Smartwatches: Some smartwatches can receive wireless power from compatible smartphones. However, smartwatch charging systems vary between models, so compatibility should be confirmed before relying on the feature.

Other smartphones: A supported smartphone may be able to share power with another phone that supports compatible wireless charging. This can be useful when someone needs enough battery power to make calls, send messages or use other essential functions.

Smaller accessories are often more practical for reverse wireless charging because they generally require less energy than a smartphone with a larger battery.

Benefits Of Reverse Wireless Charging On Smartphones

The biggest advantage of reverse wireless charging is convenience. It allows users to share battery power without carrying a separate wireless charging pad for a compatible accessory.

For example, imagine that your wireless earbuds are almost out of battery while you are travelling. If your smartphone supports reverse wireless charging and the earbud case is compatible, you can place the case on the back of the phone and allow it to receive power.

The feature can also be useful during situations where access to a charger is limited. A supported smartphone can provide temporary power to a compatible accessory or another phone instead of leaving the device completely without battery.

Another benefit is that it can reduce the number of charging accessories needed in certain situations. A smartphone can serve as an emergency wireless power source for compatible devices that support the required charging technology.

Limitations To Consider

Reverse wireless charging also has limitations that users should understand before depending on it.

One of the main limitations is charging speed. Reverse wireless charging is generally intended for low-power charging and battery boosts rather than quickly charging a completely empty smartphone. A receiving device may take much longer to charge than it would with a suitable wired charger.

There is also energy loss during wireless power transfer. Not all the energy used by the phone to transmit power will be stored in the receiving device's battery. This means the phone providing the charge can lose more battery power than the receiving device gains.

Heat can also affect charging. Wireless power transfer can generate heat and a smartphone may reduce or stop the process if its temperature becomes too high.

The distance between the devices matters as well. Their charging coils need to be close and properly aligned. If the receiving device moves away from the correct position, charging can slow down or stop.

A thick phone case may also interfere with wireless charging in some situations by increasing the distance between the charging coils.

How To Use Reverse Wireless Charging

The exact steps vary between smartphone manufacturers and software versions, but the general process is similar.

On a supported phone, users can normally find the feature in the battery, power or quick settings area. It may be labelled Reverse Wireless Charging, Wireless Power Sharing, Battery Share or another similar name.

After activating the feature, place the receiving device on the designated charging area on the back of the smartphone. The two devices should be positioned carefully so that their wireless charging coils are close together.

A charging indicator may appear when the receiving device is recognised and power transfer begins.

Users should also check the phone's battery level before starting. If the smartphone is already low on power, using reverse wireless charging may leave it with insufficient battery for its own needs.

If charging does not begin, check whether both devices support compatible wireless charging technology. Removing a thick case from either device may also help if it is interfering with the connection.

Wireless Charging And Reverse Wireless Charging Compared

Although both technologies use wireless power transfer, they perform different roles.

With wireless charging, a separate charging pad or compatible charger sends power to the smartphone.

With reverse wireless charging, the smartphone sends power from its own battery to another compatible device.

For example, placing a smartphone on a wireless charging pad is normal wireless charging. Placing wireless earbuds on the back of a supported smartphone so that the phone charges the earbuds is reverse wireless charging.

This distinction is important because a smartphone supporting wireless charging does not necessarily support reverse wireless charging. The phone needs the appropriate hardware and software to transmit power as well as receive it.

Charging Speed And Efficiency

Reverse wireless charging is generally slower than charging a device with a suitable wired charger. The actual speed depends on the power output of the smartphone, the receiving device and the wireless charging technology involved.

Efficiency is another consideration. Wireless power transfer involves some energy loss, so the smartphone providing the power may use more battery energy than the receiving device ultimately stores.

The positioning of the devices can also affect charging performance. Wireless power transfer works best when the two charging coils are close and properly aligned. Moving the receiving device away from the correct position can weaken the connection and reduce charging performance.

For these reasons, reverse wireless charging is better suited to giving a device a useful battery boost than quickly charging a completely empty smartphone.

What It Means For Smartphone Users

Reverse wireless charging can be a useful backup feature when a compatible device needs power and a conventional charger is not available. It is particularly practical for everyday accessories such as wireless earbuds that may need a small amount of extra battery while travelling or away from home.

The feature can also provide a temporary power source for another compatible smartphone. However, users should remember that the phone providing the charge will lose some of its own battery power in the process.

It is therefore important to check the smartphone's battery level before using the feature. If the phone is already running low, sharing its battery may leave it without enough power for calls, mobile data or other important tasks.

Compatibility is equally important. Not every smartphone that supports wireless charging can provide reverse wireless charging and not every wireless accessory can receive power from every supported phone.

For most users, reverse wireless charging is best viewed as a convenient way to share battery power when needed. It can be helpful in everyday situations, but a dedicated charger remains the more practical option for regular and faster charging.

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