What Is Bidirectional Charging in a Power Bank, and How Does It Work?

The same USB-C connection you use to recharge a power bank may also be able to charge your phone or another device. So how can one connection receive power at one moment and provide it the next?

That is bidirectional charging, also called two-way charging. It sounds technical, but the idea is simple: a USB-C connection designed for both power roles can work as an input or an output. This guide explains what that means, how the power role is decided, how bidirectional charging differs from pass-through charging, and why it can make power banks simpler to use.

What is bidirectional charging?

Bidirectional charging means a USB-C connection can act as either an input or an output. It can receive power to recharge the power bank or provide power to a connected device.

In everyday use, you may barely notice the change in role. Connect the power bank to a compatible charger and the connection receives power. Later, connect a compatible phone, tablet or accessory and the connection can provide power instead.

One connection can therefore handle two different jobs. On a power bank designed this way, that can reduce the need for separate input and output sockets and simplify the port layout.

However, not every USB-C port is bidirectional. USB-C and USB Power Delivery support different power roles, and the specific port or built-in cable must be designed to operate as both a power source and a power sink.

How does bidirectional charging work?

USB-C Power Delivery can support flexible power roles rather than requiring every connection to have one permanently fixed direction. A USB-C connection designed for dual-role power can therefore operate as a source when it supplies power or as a sink when it receives power.

When compatible USB-C devices are connected, the connection establishes the relevant power roles. Where USB Power Delivery is used, the devices can also negotiate supported voltage and current before higher-power charging is established.

Connect a bidirectional power bank to a compatible USB-C charger and the power bank can receive power. Connect a compatible device to the same dual-role connection and the power bank can become the power source instead.

The rated maximum input and output do not mean the connection always runs at that power. Actual charging power depends on the charger, connected device, supported charging protocols, battery level and other operating conditions.

On the MagFlow Air models discussed below, USB-C provides the wired input and output functions, while the Qi2 magnetic charging surface is used to provide wireless power to compatible devices.

Bidirectional charging vs pass-through charging

Bidirectional charging and pass-through charging describe different capabilities.

Bidirectional charging means a connection can work as an input or an output. Pass-through charging is a separate system-level feature that allows a power bank to receive power while also supplying power to another connected device.

A power bank can support bidirectional USB-C without supporting pass-through charging. Pass-through support should therefore be confirmed in the specifications for the specific model rather than assumed from an input/output rating alone.

This distinction matters because a specification such as “20 W input and output” describes the maximum supported power in each role. It does not, by itself, confirm simultaneous charging and recharging.

Why bidirectional charging matters

A two-way USB-C connection can make a power bank easier to use because the same connection can cover both recharging the power bank and charging compatible devices.

That can reduce the number of dedicated sockets a compact design needs and make it easier to use one suitable USB-C cable for more than one charging task. The exact layout still depends on the power bank, because models with multiple ports or built-in cables may assign different roles to different connections.

Older power banks often used a dedicated Micro-USB input for recharging and separate USB-A outputs for devices. A bidirectional USB-C design can combine those roles into one compatible connection instead.

In practice, you might recharge the power bank from a compatible USB-C charger, then later use the bidirectional connection to charge your phone or tablet. If you want a broader guide to input ratings, cables and charging habits, see our guide to charging a power bank.

How fast is bidirectional charging in and out?

Input and output limits depend on the individual power bank. On the two MagFlow Air capacities below, the rated maximum USB-C input and output are the same in each direction: up to 20 W for the 5,000mAh model and up to 30 W for the 10,000mAh model.

Matching maximum input and output ratings make the USB-C connection flexible in either role, but they do not mean the power bank will recharge in the same amount of time that it takes to charge another device.

Charging time depends on battery capacity, the available input power, battery level, temperature and charging conditions. UGREEN states that the 10,000mAh MagFlow Air can recharge in about two hours via its 30 W input. The current UK product information does not specify an equivalent full-recharge time for the 5,000mAh model, so no fixed time should be assumed from its 20 W rating alone.

The picks: UGREEN MagFlow Air with two-way USB-C charging

Both MagFlow Air capacities provide wired input and output alongside Qi2 magnetic charging, giving you a choice between cable-free convenience and wired charging.

The UGREEN MagFlow Air Magnetic Slim Power Bank (10000mAh, Qi2 15W) supports up to 30 W wired input and output, up to 15 W Qi2 magnetic charging, and has a 13.9 mm body. It also includes a built-in USB-C cable and an additional USB-C port.

The UGREEN MagFlow Air Magnetic Power Bank (5000mAh, Qi2 15W) supports up to 20 W USB-C input and output and up to 15 W Qi2 magnetic charging. It is 8.6 mm thick and weighs about 127 g.

You can explore more wireless magnetic power banks if you want to compare charging layouts and capacities.

To compare these two capacities in more detail, see our 5,000mAh vs 10,000mAh power bank guide. If slimness and everyday carry are your priority, our best slim power bank guide looks at the trade-offs in more detail.

The wrap-up

Bidirectional charging means a USB-C connection can switch between receiving power and supplying it when the hardware is designed for both power roles. USB Power Delivery can then negotiate supported charging levels on compatible connections.

It is different from pass-through charging: a bidirectional connection can work in either direction, but that does not automatically mean the power bank can charge itself while powering another device.

The UGREEN MagFlow Air Magnetic Power Bank (5000mAh, Qi2 15W) supports up to 20 W USB-C input and output, while the UGREEN MagFlow Air Magnetic Slim Power Bank (10000mAh, Qi2 15W) supports up to 30 W USB-C input and output. Both also support Qi2 magnetic charging at up to 15 W on compatible devices.