Why Xiaomi Redmi 9 does not include fast charging: diagnostics and repair

Introduction: why the smartphone stopped charging quickly

You've connected the Xiaomi Redmi 9 to a charger, but instead of the usual 18W, the screen says "Charge" without the "Fast" mark on the screen - or the indicator shows a slow speed at all. The situation is familiar to many owners of this budget smartphone, especially after a year or a half of operation, the reasons can lie in both banal wear and tear of accessories and hidden software failures.

In this article, we’ll look at all the possible reasons for the Redmi 9’s fast charging shutdown, from damaged cable to firmware errors. MIUI. You'll learn how to diagnose a problem yourself, what settings to check first, and when to actually go to the service center, and we'll also tell you why even the original power supply sometimes "does not pull" the declared 18 watts and how to fix it.

Important: Redmi 9 supports Quick Charge 3.0 (up to 18 watts), but it must work with several conditions – from the firmware version to the battery temperature. If at least one of them is broken, the smartphone automatically switches to standard charging mode (5-10 watts).

1. Problems with charging accessories: cable, power supply, adapter

In 60 percent of cases, slow charging is due to faulty or incompatible accessories, and even if you use Xiaomi's "native" kit, the cables wear out over time and the power supplies lose power. Here's how to check if they work:

• 🔌 Check the cable for insulation bending, melting, or damage, and pay special attention to the areas near the connectors (USB-Type-C and C). USB-A).
• 📱 Try another cable, preferably original or certified (with Quick Charge 3.0 or a new one). USB-IF).
• ⚡ Test the power supply on another device. If it doesn't deliver 18 watts (like charging another smartphone slowly), the problem is that it's not working.
• 🔄 Check the Type-C connector on your smartphone – often dust or debris accumulates inside, which worsens contact.

Advice: For Redmi 9 Suitable power supplies with Quick Charge support 3.0, Power Delivery (PD) Xiaomi Turbo Charge, the power must be at least 18 Watt (9V/2A or 12V/1.5A). If you use wireless charging, please note that Redmi 9 It is not officially supported, and any adapters will work in slow mode.

Check the cable for damage.|Test the power supply on another device|Clean Type-C connector from dust|Try the original set from Xiaomi-->

Critical: if the smartphone shows a notification when you connect the charger, "This device does not support fast charging," the problem is precisely in the accessories or the port, in which case even a serviceable power supply will not be able to transmit enough power.

2. Software failures: MIUI, kernel and background processes

Software errors are the second most common reason for fast charging shutdowns. Redmi 9 is responsible for power management:

• 📱 Firmware MIUI (version).
• 🔧 The kernel of the system that controls charging.
• 🤖 Background applications that consume resources.

How to diagnose:

1. Go to Settings. → The phone. → Version. MIUI And check the firmware's relevance. Redmi 9's latest stable version — MIUI 14 (based on Android 12).
2. Start Developer Mode (7 times click on Version) MIUI), Then go to Settings. → Additionally. → For developers → Debugging by USB and turn on the Log Charging (if available).
3. Install the AccuBattery app (from Google Play) and check the charging speed chart. If the power doesn't go above 10 watts, it's a software problem.

Decisions:

• 🔄 Reboot your smartphone – sometimes background processes block fast charging.
• 🗑️ Clear the cache through Settings → Memory. → Clear the cache.
• 📲 Update. MIUI Up to the latest version or roll back to a stable build if the problem appears after the update.
• ⚙️ Reset the settings to factory (pre-make a backup!).

Regularly, right after the exit|Only if there are bugs.|Never, I'm afraid of failure.|I don't know how to update.-->

⚠️ Note: If after the update MIUI The smartphone began to charge slowly, and in the settings appeared the item "Battery" → Charging Optimization Mode -- Turn it off. This feature artificially limits current to extend battery life.

3.Overheating or low temperature: how it affects charging

Xiaomi Redmi 9 automatically reduces the charging speed if the battery temperature goes beyond 10-45°C. It may not display an overheating warning on the screen:

How to measure temperature:

1. Install the AIDA64 or CPU Monitor app.
2. Connect the charging and open the "Temperature" section.
3. If the battery value is above 35°C, let the smartphone cool for 10-15 minutes.

What to do when overheating:

• 🌡️ Remove the cover – it can block heat transfer.
• 🚫 Do not use your smartphone while charging (games, video, navigator).
• 🔥 Check the charging unit – cheap adapters often overheat themselves and heat the cable.
• ☀️ Avoid direct sunlight and charging near heat sources.

💡

If the smartphone is heated even without charging, check the work of the processor in the AIDA64. Maybe some app loads it 100% in the background.

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

The Lithium Polymer batteries in Redmi 9 are designed to last 500 to 800 charge cycles, and then their capacity drops by 20 to 30 percent, and the controller starts to limit current for safety.

• ⚡ Smartphone discharges in 3-4 hours with moderate use.
• 📉 B Settings → Battery → Battery condition capacity shows less than 80% of the original.
• 🔋 When you connect the charging, the percentage first jumps (for example, from 10% to 20%), then falls back.
• 🛑 Fast charging is turned on only for 10-15 minutes, then goes into slow mode.

How to check the wear:

1. Install AccuBattery and look at the Health setting.
2. If the value is below 80%, the battery needs to be replaced.
3. Enter ##4636### in the dialer, select Battery Information and check Charge Level and Status.

What to do:

• 🔧 Calibrate the battery: completely discharge the smartphone (before turning off), then charge to 100% without interruptions.
• 🔄 Reset the power controller settings (sometimes helps when crashes occur).
• 🛠️ Replace the battery in the service center.The cost for the Redmi 9 is about 1500-2500 rubles (with work).

⚠️ Note: if the battery capacity in AccuBattery shows less than 70%, and the smartphone turns off at 20-30% charge, this is critical wear.

5. Power controller failures: hardware malfunctions

Charging controller (PMIC — Power Management IC) — It's a chip that regulates the current flow to the battery. If it fails, the smartphone can do it:

• 🚫 No charge at all.
• ⚡ Charge only when switched off.
• 🐢 Work in slow mode even with the original power supply.

Causes of PMIC failure:

• ⚡ Voltage surges (for example, when using poor-quality charges).
• 💦 Moisture on the motherboard.
• 🔥 Overheating due to prolonged play or exercise.
• 🛠️ Failed repair (for example, after replacing the Type-C connector).

How to diagnose:

1. Connect your smartphone to your PC and check if it is detected in Device Manager.
2. Try charging the Redmi 9 from another power supply (e.g., a laptop).
3. If the smartphone is charged only in the off state - this is a sure sign of a problem with the device. PMIC.

Decisions:

• 🔧 Fastboot your smartphone (sometimes helps with controller software failures).
• 🛠️ Replace. PMIC The cost of repairs - from 3000 rubles.
• 📱 If the smartphone is guaranteed – contact the official service Xiaomi.

External factors: moisture, mechanical damage, dirt

Even if the accessories and battery are fine, fast charging may not work due to external reasons:

• 💧 Moisture entering the Type-C connector or board. Redmi 9 does not have official protection by standard IP, Therefore, even a small humidity can cause corrosion of contacts.
• 🧹 Contamination of the connector with dust, pile or metal shavings (for example, after repair).
• 🔨 Mechanical damage after falls (for example, detachment of contacts on the board).
• ⚡ Static electricity that can damage the charging controller.

How to check:

1. Light the Type-C connector with a flashlight – there should be no debris or oxidation inside.
2. Blow into the connector or gently clean it with a wooden toothpick (not metal objects!).
3. If your smartphone fell or got wet, check the moisture indicators (small white stickers inside the connector and under the lid). If they turned red, there was moisture.

What to do:

• 🚿 If water hits, turn off your smartphone immediately, remove it. SIM-card and battery (if possible), then dry in rice or silica gel for 24-48 hours.
• 🧴 Use alcohol to clean your contacts (90%+) Do not use acetone or other solvents!
• 🛠️ For mechanical damage, contact the service - self-repair can aggravate the problem.

💡

If the moisture indicators are red, but the smartphone is working, it does not mean that the problem is solved. Corrosion can manifest itself in weeks or months, so it is better to show the device to a specialist.

7. Energy saving settings and hidden functions MIUI

Redmi 9 has a few hidden features that can block fast charging, often turned on by default or activated accidentally:

• 🔋 "Charging optimization" - limits current to extend battery life. → Battery → Battery settings.
• 🌙 "Sleep mode" - disables background processes and can affect charging. → Screen. → Sleep regimen.
• ⚡ "Fast Charging Manual. Some firmwares need to be enabled separately: Settings → Battery → Fast charging.
• 🔄 "Adaptive charging" - takes into account the user's habits and can artificially slow down the process. → Battery → Adaptive charging.

How to disable restrictions:

1. Go to Settings. → Battery → Battery settings and deactivate all optimisation options.
2. B Settings → Special facilities → Battery optimization check if system applications are added (e.g, MIUI Optimization).
3. Reset the battery settings: Settings → Battery → ⋮ (menu) → Reset the settings.

If after these actions fast charging did not work, try to reset all settings to factory (don’t forget to make a backup!).

FAQ: Answers to Frequent Questions