Smartphones are no longer just devices for calls and the Internet, becoming universal tools that can support other gadgets. Xiaomi’s Redmi Note 9 Pro was one of the first mid-range devices to offer advanced energy saving and power sharing, a feature known as OTG (On-The-Go) or reverse charging that allows the phone to be used as an external battery for headphones, smartwatches or other smartphones.
Many owners face a situation where connecting a second device via a cable does not lead to the desired result.This is often due to the fact that in the MIUI shell, activating a USB port for power transmission may require manual intervention or specific settings. Reverse charging is a convenient way to not be left without communication at a critical time, but it requires an understanding of the principles of the USB-C interface.
In this article, we will discuss in detail how to activate the power mode on the Redmi Note 9 Pro, which cables are suitable for this task, and how to avoid errors that can lead to the discharge of both devices.
Principles of OTG and features of the model
USB On-The-Go technology allows mobile devices to act as a host, that is, a power source for the periphery. In the case of the Redmi Note 9 Pro, the hardware fully supports the output of 5 volts via the USB-C port. However, the MIUI software by default may not activate this mode immediately after connecting the cable, waiting for commands from the user or conditions.
The power controller in Xiaomi smartphone automatically determines the type of device connected. If it is a flash drive or keyboard, the data mode is turned on. If another smartphone or battery is connected, the system should switch to the current supply mode. It is important to understand that the power transfer rate is limited by the USB 2.0 standard that is implemented in this port, so you should not expect a quick charge of another device.
There is a common misconception that the function requires a special adapter.In fact, the Redmi Note 9 Pro features a Type-C port that is symmetrical and supports reverse currents when using a quality Type-C cable or a Type-C adapter - USB-A.
⚠️ Note: Using cheap cables without shielding can lead to unstable operation of the power controller and false alarms, which will constantly interrupt charging.
To successfully activate the process, the battery level of the donor smartphone itself must be sufficient.The MIUI system blocks the output of power if the battery is discharged below a certain threshold, usually 15-20%, to keep the main device running.
Preparation of equipment and compatibility check
Before you try to charge another device, you need to make sure that the accessories used are in good working order. The cable plays a key role in the power transfer process. Not all Type-C cables are the same: some are designed only to charge the phone itself and do not fully support data transfer or reverse current.
It is recommended to use the original cable from the Xiaomi supply kit or certified analogues labeled 3A (3 Amps). Such cables have thicker veins, which reduces the voltage drop when transferring current to another device.
- 🔌 Cable type: Use Type-C – Type-C cable for maximum compatibility or quality adapter OTG.
- 🔋 Charge level: Make sure that the Redmi Note 9 Pro charged at least to the minimum 30-40% before the beginning of the procedure.
- 🧹 Port cleanliness: Check the connector USB-C dust and pile, which can prevent close contact.
If the Xiaomi smartphone is overheated or, conversely, is in extreme cold, the system can temporarily limit the current output to protect the battery. The optimal temperature for electronics is in the range of 10 to 35 degrees Celsius.
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Before connecting another device, wipe the USB-C connector with a soft dry cloth – oxidation of the contacts is often the reason for the lack of system response.
Step-by-step instruction: how to turn on the function
Unlike some other manufacturers, Xiaomi did not put the reverse charging button on a prominent spot in the default notification curtain in older versions of MIUI. However, in newer interface updates, this option may have appeared.
Unlock your smartphone screen and swipe from top to bottom, open the control center. Find an icon that says "Reverse Charging" or "Reverse Charging." If you don't have one, you need to activate the feature via the engineering menu or USB settings, as a direct switch may not be available in your firmware version.
☑️ Activation algorithm
The main method of activation on the Redmi Note 9 Pro is often to connect the cable to the smartphone and then to the device to be charged. If charging didn't go automatically, try the following sequence of actions through the developer menu, which sometimes requires forced activation.
Go to Settings → About Phone and quickly click 7 times on MIUI Version. Once you have the message “You are a developer”, go back to the main settings menu, select Additional → For Developers. Find the item associated with the default USB configuration and try to change it, although in most cases MIUI itself manages this process.
⚠️ Note: Do not change the settings in the developer menu unless you are sure of their purpose, as this can lead to unstable system operation or data loss.
If software activation is not required, the process should begin immediately after the connection. The screen of the donor smartphone may flash or emit a characteristic connection sound. USB-At this time, the indicator of the set of capacity should appear on the screen of the charging gadget.
Configure USB settings in MIUI system
MIUI has flexible USB port behavior settings. In some cases, the smartphone defaults to Charge Only mode, ignoring the connected device as a power consumer, and to fix this, you need to manually switch port mode.
Connect the Redmi Note 9 Pro to a computer or other device. After a few seconds, the notification curtain will show the message “Charge through” USB». Click on this notification. The "Use" menu will open. USB», where to select "File Transfer" or «USB-modem, which sometimes causes the port to issue voltage.
However, for clean reversible charging without data transfer, the most effective way is to use third-party triggering apps if standard methods don’t work. Applications like the USB OTG Helper can force the controller to turn on the host mode.
| USB mode | Description | Impact on charging |
|---|---|---|
| Just charging. | The port consumes energy | Reversible charging is not possible |
| File Transfer (MTP) | Data exchange from PC | Often activates the current output |
| USB-modem | Internet distribution | Stable issuance of 5B |
| MIDI | For musical instruments | Not recommended for charging |
It is worth noting that the Quick Charge protocol is usually not activated when reversing.The smartphone will give a standard 5 volts and a current strength of about 0.5-1 Ampere, which is safe for most small gadgets, but slow for capacious batteries.
Why does not fast charging work when reversed?
What to charge from the Redmi Note 9 Pro
The power output of the Redmi Note 9 Pro is limited, so the list of devices that can be efficiently charged also has its limits, primarily accessories with a small battery capacity.
Wireless headphones like AirDots or Mi True Wireless Earbuds charge from your smartphone without problems. Mi Band fitness bracelets and smartwatches are also great. For smartphones, this feature will be a rescue in an emergency, allowing you to gain 10-15% of charge for an important call.
- 🎧 Audio: TWS-headphones, portable speakers with a small battery.
- ⌚ Wearable electronics: Smart watches, activity trackers, e-cigarettes (with caution).
- 📱 Smartphones: Other phones for emergency charge recharge (slow).
It is not recommended to try to charge tablets or laptops, as the current issued by Xiaomi will not be enough to cover the power consumption of these devices in active mode, and charging will either not go or will be extremely slow.
Possible problems and ways to solve them
Even if you follow all the instructions, users can run into difficulties, and the most common problem is that the phone connects, makes a sound, but it doesn't charge, and this may be due to software freezes on the USB service.
In this case, a simple reboot of the Redmi Note 9 Pro device will help. If the problem persists, try clearing the cache of the system application "Settings" or resetting the network settings, which sometimes resolves driver conflicts. It is also worth checking whether the power saving mode is turned on, which can block background processes associated with current output.
Another cause could be damage to the USB-C port itself. Frequent use of various devices to connect leads to mechanical wear and tear of the contacts. If the cable staggers or falls out, the problem may be physical, and software methods will not help.
⚠️ Attention: If the port USB-C loosened or moisture got inside, it is strictly forbidden to try to charge other devices - this can cause a short circuit and the motherboard out of order.
In rare cases, the problem lies in the device that is being charged, which is not correctly determining the power source. Try connecting another gadget to the Redmi Note 9 Pro for diagnostics. If the second phone is charging, then the problem is in the first device or its cable.
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If no cable helps to activate the current output, most likely, the power controller or the USB port itself in the smartphone is defective, which requires contacting the service center.
Effects of reverse charging on the battery
Using a smartphone as a power bank affects the state of its own battery, and the energy return process is accompanied by heating the device, as the voltage is converted and the controller is operated under load.
Regular use of the reverse charging function can accelerate the degradation of Xiaomi’s battery.The deep discharge cycles that can occur when charging other devices to the point of exhaustion of its own life are also harmful to battery chemistry.
However, if you use the function moderately, only if necessary, there will be no serious harm.The modern controllers in the Redmi Note 9 Pro are equipped with overheating and overload protections that will turn off the current output when critical values are reached.
Try not to play heavy games or watch videos while dispensing energy, so as not to aggravate the heating of the case. Keep your smartphone on a hard surface for better heat sink.