Why fast charging on Xiaomi Mi 9 does not work: a full analysis of the causes and solutions

Xiaomi Mi 9 is the flagship of 2019, which is still relevant thanks to powerful hardware and support for updates. However, many owners face a problem: the smartphone suddenly stops charging quickly, despite the original power supply and cable. In some cases, the charging speed drops to 5W (like normal ones). USB-Ports, and sometimes the device refuses to recognize charging as “fast».

The causes of this phenomenon can be found in software failures (for example, after the MIUI update) and hardware malfunctions, from battery wear to damage to the power controller. In this article, we will analyze all possible scenarios, offer diagnostic tests and give clear instructions for fixing the problem, focusing on the hidden MIUI settings that affect charging, but about which few people know.

1. Checking the charger and cable: where to start the diagnosis

The first thing to rule out is a charging kit malfunction, and even Xiaomi's original accessories fail over time, especially if they're actively used.

• 🔌 Test with another charger. Take the power supply from another Quick Charge 4-enabled smartphone+ (For example, from Xiaomi Mi 10 or POCO F3). If fast charging is working, the problem is with your original charging system.
• 🔗 Check the cable.Try charging the Mi 9 via another cable (preferably original or certified). USB-C). Cheap cables often don’t support high currents.
• 📱 Diagnostics on another device. Connect your power supply to another Quick Charge smartphone. If it's also charging slowly, the charger is malfunctioning.

Pay attention to the physical condition of the connectors: oxidation, contamination or mechanical damage can disrupt contact. Use a wooden toothpick (not metal!) and alcohol to clean. Also check if the USB-C connector in your smartphone is a sign of wear and tear on the socket.

⚠️ Warning: Never use chargers with higher output voltage 9V/2A (maximum 9 — 18W). Connection to power supply units on 30W+ (For example, from laptops, can damage the power controller!

2. Software glitches: why MIUI blocks fast charging

Often the problem is not the hardware, but the MIUI firmware. After updating or resetting the settings, the system may misidentify the type of charger or artificially limit the current.

• 📲 Reset charging settings. Go to Settings → Battery → Battery settings → Reset the charging settings. That will bring the power back to factory values.
• 🔄 Related: Retreat of the update MIUI. If the problem has appeared after the update, try to roll back to the previous version of the firmware via Fastboot (instruction below).
• 🛠️ Clear the system cache. Go to Settings. → Memory. → Clean up and select "Clear system cache" to help if the failure is caused by corrupted temporary files.

Another common reason is the activated power saving mode, and even if you didn't manually turn it on, MIUI can automatically limit charging when the battery is low or the temperature is high, to turn it off:

1. Open the Settings. → Battery.
2. Click on the icon. ⚙️ top-right.
3. Turn off the Smart Energy Saving and Charging Limit options.

Battery wear: when it's time to change the battery

Xiaomi Mi 9 is equipped with a battery capacity of 3300 mAh, which after 300-500 charging cycles begins to degrade. If your smartphone has served more than 2-3 years, the problem may be the loss of battery capacity.

• 🔋 Smartphone discharges in 3-4 hours with moderate use.
• 🌡️ The battery is very hot even with normal charging.
• ⚡ Charging speed drops to 5W despite original charger.
• 📉 B Settings → Battery → The battery status is below 80%.

You can check the actual battery capacity using applications like AccuBattery (available on Google Play). If the program shows wear and tear of more than 30%, it is time to change the battery. The original battery for the Mi 9 has the article MBJ405730 (you can order on AliExpress or in service centers).

⚠️ Warning: If you choose to replace the battery yourself, use only original or certified batteries with a thermal sensor. Cheap analogues may not support fast charging or even swell!

4. Power controller damage: how to diagnose

The Power Controller (PMIC) is a chip that controls the charging and distribution of power in a smartphone. If it fails, the Mi 9 can:

• 🔌 Not to recognize the charger at all.
• ⚡ Only charge 5W despite the original unit.
• 🔄 Disconnecting spontaneously from charging.
• 🌡️ Overheat in the lower part of the body.

Diagnosing a PMIC problem at home is difficult, but there are indirect signs:

1. The smartphone does not turn on without a connected charger.
2. When connected to a PC, it is defined as an “Unknown Device”.
3. Charging is in jerks (current jumps from 0 to 1000 mA).

If you suspect a controller malfunction, the only solution is repairs at the service center. PMIC It requires a soldering station and experience with microelectronics. The cost of repairs in official Xiaomi services is 3000-5000. ₽ (depending on the region).

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Before visiting the service center, back up your data via Mi Cloud or ADB. After repairing the power controller, you may need to reset your settings!

5. Hidden MIUI settings: how to enable fast manual charging

V MIUI There are hidden options that can block fast charging, for example, after an upgrade, the system sometimes drops the flag. fast_charge_enabled. To check and turn on:

1. Activate Developer Mode: Go to Settings → About Phone and click on MIUI Version 7 times.
2. Back to Settings → Additionally. → For developers.
3. Find the Debugging by USB and turn it on.
4. Connect your smartphone to your PC and execute the command: adb shell settings put global fast_charge_enabled 1

Also check the following parameters:

• 🔧 settings put global battery_charge_limit 0 — discharges.
• 🔧 settings put global thermal_engine_enabled 0 — Disables thermothrottle (temporarily!).

If you've had this manipulation, the problem was the software restriction, but be careful: turning off the thermal control could cause you to overheat!

Check the charger and cable|Reset the battery settings in MIUI|Turn off the power saving mode|Check the battery wear through AccuBattery|Activate hidden settings through ADB-->

6. Effect of temperature and humidity on charging

Xiaomi Mi 9 automatically reduces charging speeds in extreme temperatures (below 0°C or above 45°C).This is battery damage protection. If your smartphone overheats while charging, try:

• 🌬️ Charge the device in a ventilated room (not in the sun or under a blanket).
• 📵 Disable all background processes (especially games and navigation).
• 🔋 Remove the cover - it can worsen the heat sink.
• ❄️ If your smartphone is cold (like after the street in winter), let it warm up to room temperature.

Fast charging can also be turned off when humidity is high (for example, if you use your smartphone in the rain or in the bathroom).

1. Turn off the device and dry it in rice or silica gel for 12-24 hours.
2. Check the moisture indicator (white circle in the tray for the SIM-cards) – if it is red, do not turn on the smartphone until completely dry!

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If the Xiaomi Mi 9 overheats when charging, never continue the process – it could cause the battery to bloat or damage to the motherboard!

7. Alternative charging methods: what to do if nothing helps

If all of the above methods fail, try alternative methods:

• 🔄 Wireless charging. Mi 9 supports Qi standard (up to 20W). Use a certified charging pad (e.g. Xiaomi Wireless Charging Pad).
• 💻 Charging through USB-PC ports. Speed will be low (5W), but it's better than no charging at all.
• 🔋 Power Bank with Quick Charge support.Some external batteries (e.g. Xiaomi Mi Power Bank 3 Pro) can produce 18W.
• 🛠️ Hand-held firmware charging module, rarely helps flashing PMIC through EDL-regime (experience required!).

If you decide to use wireless charging, consider:

• The speed will be lower than that of the wired one (maximum 20W vs. 27W of the original unit).
• The smartphone can get warmer due to induction losses.
• Do not put metal objects (coins, keys) on the charging pad - this can damage the coil.

FAQ: Frequent questions about fast charging Xiaomi Mi 9