Why Xiaomi Redmi 9 is charging for a very long time: a full analysis of the causes and solutions

Owners of Xiaomi Redmi 9 They often have problems with slow charging: instead of promised 1-2 battery 100% post 4-6 or even "suspends" on the 80%. The reasons can be both hardware malfunctions (battery wear, damaged cable) and software failures (background processes, incorrect settings). In this article, we will discuss all possible factors affecting the charging speed of Redmi. 9, including hidden parameters MIUI Features of the Mediatek Helio Power Controller G80.

It's important to understand that if you used to charge your phone fast, and now you're saying "brake" is a problem signal, we're not going to just stop with the corny tips like "change charge," instead you're going to get a step-by-step diagnostic with tests, comparison tables and instructions for all sorts of scenarios, from changing the cable to calibrating the battery through the engineering menu.

1. Technical Charging Specifications of Redmi 9: What Xiaomi Promises

Xiaomi Redmi 9 officially supports fast charging 18W (Quick Charge 3.0, but the package includes an adapter for the 10W. This is the first catch: many users do not even suspect that their phone is capable of charging 2 times faster:

• 🔋 Battery capacity: 5020 mAh (typical) / 5000 mAh (minimum).
• ⚡ Maximum charging power: 18W (Compatible adapter is required).
• ⏱ Full charge time: ~2 hours (c) 18W-adapter ~3 hours (c) 10W-box-mounted).
• 🔌 Type of connector: USB Type-C (but not all cables support) 18W!).

If your Redmi 9 charges for longer than 3 hours with the original adapter, that's a deviation. 18W The first thing you need to check is the actual charging power.

2. Hardware causes of slow charging

At the physical level, the charging speed depends on four components: power adapter, cable, port. USB-C Let's take each of them apart.

Problems with the power adapter

Even if it says on the adapter «18W», It doesn't guarantee real power. Cheap Chinese charging systems often only give you power. 50-70% from the claimed:

1. Connect your phone to charging and go to Settings → Battery → Battery status.
2. See the current charging power (in mW or W). 5W — adapter malfunction.
3. Use the Ampere app (available in the Play Market) to accurately measure current and voltage.

Critical signs of a faulty adapter:

• 🔥 Heating the adapter to a temperature above 50°C (can be checked by infrared thermometer or by touch).
• ⚡ Blinking the charging indicator on the phone (they talk about unstable voltage).
• 📉 Falling charging power to 0.1-0.5W through 10-15 minutes after connection.

Wear or damage to the cable

Cable USB-C — The most vulnerable link, and over time, his veins become oxidized and his contacts loosen:

• 🔄 Charging is interrupted at the slightest movement of the cable.
• 🐢 The charging speed drops if you bend the cable in a certain place.
• 🔌 The phone defines the connection type as "charging through" USB" (Not "Fast Charging").

For the test, take a cable that is known to be in good working order (like a different device) and compare the speed. If the new cable is charging faster, the old one should be replaced. USB-C Support Quick Charge 3.0. Look for the label USB-C to USB-C or USB-A to USB-C (QC 3.0).

Pollution or damage to the port USB-C

Redmi 9 port is not protected from dust and moisture (no certification) IP). Garbage or contact oxidation leads to poor contact. How to clean the port:

1. Turn off the phone.
2. Light the port with a flashlight and remove the trash with a plastic (not metal!) toothpick.
3. Wet the cotton swab in isopropyl alcohol (not in water!) and gently wipe the contacts.
4. Let the port dry. 10-15 minutes before connection.

⚠️ Warning: Do not use compressed air to clean the port - this can drive dust deeper. Also avoid metal objects: they scratch the contacts and can close the port.

Battery degradation

Lithium polymer batteries lose capacity after 300-500 For the Redmi, the charge cycles. 9 roughly 1.5-2 year of active use, signs of wear and tear:

• 📊 B Settings → Battery → Battery status indicated health below 80%.
• ⚡ The phone's running out of power. 4-5 hours of normal use (previously kept the day).
• 🔋 Charging "hangs" on 80-90% It's not going anywhere.

Check the status of the battery through the engineering menu:

##4636## → Battery → Status

If the health value is below good, it's time to change the battery.Average battery life in Redmi 9 — 2-3 And then you have a year of heavy use, and then you drop the capacity. 30-40%, a) the charging speed is reduced in 1.5-2 once.

3. Programmatic reasons: why MIUI brake

Operating system MIUI (version 12-14) It's actively controlling power, sometimes overly restricting charging. Here are the key brakes»:

Battery optimization and background processes

By default. MIUI It involves aggressive battery optimization, which limits the background, and paradoxically, it saves charge, but it slows charging, because it spends resources monitoring applications:

1. Go to Settings → Battery → Battery Optimization.
2. Select No Limits for Critical Applications (Messengers, Navigators).
3. Turn off Adaptive Charging in Settings → Battery → Additionally.

Also check the auto-run of the applications:

• 📱 Settings → Annexes → Auto-start.
• 🔄 Turn off autoplay for unnecessary apps (especially games and social media).

Failures in the operation of the power controller

Mediatek Helio chip G80, The one installed in Redmi 9 has a built-in power controller that sometimes "gluts:

• ⚡ The charge is coming in jerks (thereby) 10W, piece 2W).
• 🔄 The phone suddenly stops charging, although the adapter is connected.
• 📉 The percentage of charge "jumps" (for example, from 50% to 30%).

Decisions:

1. Rebooting the phone – sometimes helps to reset the controller.
2. Resetting battery settings: Settings → System system → Additionally. → Resetting settings → Resetting battery settings
3. Update of the firmware - in new versions MIUI Frequently fixing food bugs.

3.3 Viruses and malware

Some viruses (e.g. Trojan.AndroidOS.Loapi) disguise themselves as system processes and consume up to 30% of the charge per hour.

• 📈 Unexplained battery consumption in standby mode.
• 🔥 Overheating phone without load.
• 📦 Appearance of unknown applications in Settings → Annexes.

How to check:

1. Install Malwarebytes or Dr.Web Light from the Play Market.
2. Run a deep scan.
3. Check the list of running processes in Settings → The phone. → Version. MIUI → Version kernel (tap 5 times on the "Version Core" to access hidden processes).

💡

If the phone starts to charge slowly after installing a new app, remove it and check the charging speed. APK.

External factors: temperature, humidity, magnetic fields

The Redmi 9’s charging speed is highly dependent on external conditions, with the manufacturer stating the optimal temperature range for charging: 10–35.°C. When going beyond these limits, the controller automatically reduces the current.

Overheating or hypothermia

If the phone is heated above 40°C (e.g., in the sun or during play), charging can stop completely before cooling.°C. How to check:

• 🌡️ Install the app AIDA64 Check the battery temperature in the Battery section.
• ❄️ If the temperature is higher 45°C - let the phone cool down 15-20 minute.
• ☀️ Do not charge your phone in direct sun or near heat sources (battery, heater).

Humidity and corrosion of contacts

Redmi 9 has no water protection (IP-No certificate; moisture entering the port USB-C Or under the body causes the contacts to oxidize:

• 💧 The appearance of a green raid on the contacts of the port or battery.
• ⚡ Unstable charging (it goes, it doesn’t).
• 🔌 Error "Moisture in the port" when connecting charging.

If the phone has been in the water:

1. Turn it off immediately and remove the battery (if possible).
2. Wet with a napkin, don't rub it!
3. Place the phone in a silica gel bag (from shoeboxes) for 24 hours.
4. Do not turn on your phone until you make sure it is completely dry.

⚠️ Warning: Don't use a hair dryer or microwave to dry! hot air will hurt the board. Also avoid rice - it doesn't absorb moisture efficiently and can clog the port.

Effects of magnetic fields

Few people know, but strong magnetic fields (such as from wireless charging, speakers or microwaves) can interfere with the operation of the power controller.

• 🎵 Magnet column (e.g., magnet column, JBL Charge).
• 🔌 Wireless charging (even if you use a wired charger).
• 📡 router or modem.

Try to remove the source of the field and check the charging speed.

5.Diagnostics and tests: how to measure the real charging speed

To make an objective assessment of the problem, you need to measure the actual charging parameters.

• 📱 Ampere app (to measure current and voltage).
• ⏱️ Stopwatch (you can use a standard phone timer).
• 📊 Paper and pen for recording data.

Step-by-step test:

1. Unload the phone before 5-10%.
2. Connect the charger and start the Ampere.
3. Write down the current (mA) and voltage (B) values every 10 minutes.
4. Repeat the test with different adapters and cables.

If your scores are very different from the norm, there is a problem. 18W-The current does not rise above 500 mA, either the cable, port or power controller is to blame.

Use the original adapter 18W|Testing another cable USB-C|Clean up the port of garbage|Disable battery optimization in MIUI|Check the battery temperature-->

6.How to speed up the charging of Redmi 9: practical solutions

If the diagnosis reveals a problem, here are the specific steps to fix it (from simple to complex):

Quick decisions (5-10 minutes)

• 🔌 Change the adapter and cable to the obviously serviceable (for example, from the Redmi Note 10).
• 🔄 Reboot the phone – it will reset the temporary controller failures.
• ❄️ Refrigerate your phone (if it’s hot) before charging.
• 📴 Turn on the plane mode - this will turn off background processes.

Programming fixes (30–60 minutes)

1. Turn off adaptive charging: Settings → Battery → Additionally. → Adaptive charging → Turn it off.
2. Reset the battery settings: Settings → System system → Additionally. → Resetting settings → Resetting battery settings
3. Update. MIUI: Settings → The phone. → Updating the system
4. Check for viruses with Malwarebytes.

Hardware solutions (require tools)

• 🔧 Replacement of cable or adapter (cost: 300–1000) ₽).
• 🔋 Battery replacement (cost: 1500–2500) ₽ service).
• 🔌 Cleaning/replacement of the port USB-C (cost: 1000–2000 ₽).
• 📱 Replacement of the power controller (cost: 2500-4000) ₽).

When to contact the service:

• If after all the manipulations, the charging speed has not changed.
• If the phone has stopped charging at all.
• If the battery is swollen (see the rear cover raised).

💡

If the Redmi 9 charges slowly only when the screen is on, the problem is background processes. If it is slow even when it is off, the iron (cable, port, battery) is to blame.

7. Myths and misconceptions about Xiaomi charging

There are a lot of tips on the Internet that are not only not helpful, but also harmful.

7.1. “You need to discharge the phone to 0% before charging”

❌ Lithium polymer batteries have no memory effect, and deep discharge only shortens their lifespan. The optimal charging range is 20 to 80%.

7.2. “Charging from the computer is safer”

❌ USB-The computer ports only give 0.5–1A, It's 2 to 5 times slower than the adapter, and many laptops limit the current when charging other devices.

“Wireless charging faster than wired charging”

❌ Redmi 9 doesn’t support wireless charging officially. Even if you use the Qi adapter, the speed will be 3-4 times lower due to induction losses.

7.4. “You must turn off the phone while charging”

❌ Modern smartphones can charge when they're off no faster than when they're on. But airplane mode does speed things up because it shuts down the communication modules.

7.5. “The higher the amperes, the faster the charging”

❌ Speed depends on power (W), not just current. Formula: Power (W) = Voltage (B) × Current (A). For example, 9V × 2A = 18W (fast, and 5V × 2A = 10W (slowly).

8. Frequently Asked Questions (FAQ)