12 reasons why Xiaomi Redmi Note 9 started to glittle – and how to fix it

Xiaomi Redmi Note 9 is one of the most popular budget smartphones of 2020, but even it is not immune to failures. If your device suddenly starts to slow down, spontaneously reboot or give out errors, do not rush to carry it to the service center. In 80% of cases, the problem can be solved by yourself without special skills.

This article will help you understand why the Redmi Note 9 is buggy, from overheating to serious hardware malfunctions. We have collected current data for 2026, including typical model “diseases”, diagnostic methods and step-by-step instructions, and focused on software failures after MIUI updates, which often cause unstable work.

Importantly, if the phone is released before 2021, some of the problems may be related to battery wear or outdated firmware, and there is a separate section on hardware diagnostics in the article — don’t miss it if standard methods don’t work.

1. CPU overheating is the most common cause of glitches

The Redmi Note 9 is powered by a MediaTek Helio G85 processor that is prone to overheating under intense stress, and if the phone starts to slow down, shut down, or lie down while playing, shooting videos, or charging, that's the first reason.

How to check the temperature:

• 🔥 Install the app AIDA64 (Free on Google Play and open the Sensors section → Temperature, normal: up to 45.°C in plain, up to 60.°C under load. If higher, overheating.

What to do:

• 🛠️ Remove the case (especially silicone) – it blocks the heat sink.
• 🧹 Clean the charging and speaker connector from dust with a toothpick (not metal objects!).
• 🔄 Reduce the load: Turn off background apps in Settings → Annexes → Auto-start.
• 🔋 If the phone warms even in simple - reset the settings to factory (instructions below).

⚠️ Note: If the processor temperature exceeds 70°C, turn off the phone immediately! Prolonged overheating causes the chip to detach from the board -- a permanent defect that requires replacement of the motherboard (~60% of the cost of a new phone).

2. Failures after the MIUI update - how to roll back firmware

Xiaomi regularly releases updates for the Redmi Note 9, but sometimes they bring more problems than good.

• 🐢 Strong interface braking (especially when swiping up/down).
• 📵 Mobile network or Wi-Fi is lost.
• 🔄 Self-involved reboots.
• 🎵 The sound in the speakers disappears.

The first thing to do is to clear the system cache:

1. Turn off the phone.
2. Press Volume Up + Power before the Mi logo appears.
3. From the Recovery menu, select Wipe & Reset → Wipe Cache.
4. Confirm the action and restart the phone.

If that doesn’t work, try reversing to the previous version of MIUI:

Instructions:

1. Download the desired firmware version (e.g. MIUI 12.5 instead of 13/14) and rename the file to update.zip.
2. Put the file in the root of the phone’s memory.
3. Go to Settings → About the phone → System update.
4. Click on the three dots in the upper right corner → Select a firmware file.
5. Select update.zip and confirm the installation.

⚠️ Attention: Firmware rollback erases all data! If you haven't done a backup, use Mi PC Suite for Recovery of Contacts and Photos After the Procedure.

3. Battery wear - the hidden cause of shutdowns

The Redmi Note 9 comes with a 5020 mAh battery, but after 3-4 years, its real capacity drops to 60-70% of its face value.

• 🔋 Sudden shutdowns when 20-30% charge.
• 🐢 Slow charging (especially if you use a non-original cable).
• 🔥 Overheating during charging.

How to check the status of the battery:

1. Install AccuBattery (free on Google Play).
2. Charge the phone to 100% and discharge to 0% without connecting the charger.
3. Open the Health tab – if the capacity is below 3,500 mAh, it is time to change the battery.

Ways to extend the life of the battery:

• 🔌 Don’t keep your phone on charge all night – turn it off when you’re on it. 80-90%.
• ☀️ Avoid overheating (do not leave in the sun or near heaters).
• 🔄 Calibrate the battery once every 3 months: fully discharge, then charge to 100% without interruptions.

If the capacity has fallen below 3,000 mAh, it is better to replace the battery. The cost of the original battery for the Redmi Note 9 is about 1500-2000 rubles (2026), Self-replacement is possible, but requires care: you need plastic mediators to open the case and hair dryers to soften the adhesive.

💡

Before replacing the battery, check it for authenticity! the original Xiaomi battery has a hologram with a serial number and QR-code that can be checked on the manufacturer’s website.

4.Memory Lack - Why the phone is braking for no reason

Redmi Note 9 came in versions with 3/64 GB, 4/64 GB and 4/128 GB of memory. Even in the maximum configuration, the free space ends over time, which leads to:

• 🐢 Slowing down the opening of applications.
• 📱 Unintentional closure of programs.
• 🔄 Freezes when shooting photos/video.

How to make room:

1. Delete the app cache: Settings → Apps → [Select the app] → Clear the cache.
2. Move your photos and videos to the cloud (Google Photos, Mi Cloud) or to your PC.
3. Remove unused apps (especially games, which take up to 2 to 5 GB each).
4. Use it. SD-Up to 512GB card for storing media files.Important: Redmi Note 9 supports microSD up to UHS-I (Don’t buy cards faster – they won’t give you any speed boost).

If you have less than 5GB of free space, the system will start to hang because of the lack of space for temporary files, and the optimal reserve is 10-15% of the total memory.

5. Viruses and malware - a hidden threat

Even if you don’t install programs from left-handed sites, viruses can get in through:

• 📎 Investments in WhatsApp/Telegram (especially.apk files).
• 🌐 Fake websites with “free” movies or games.
• 📱 Installation of modified firmware (custom) ROM).

Signs of infection:

• 📈 Unexplained traffic consumption (check in Settings) → SIM-maps and mobile networks → Traffic consumption).
• 🔋 Fast battery discharge in standby mode.
• 📱 Appearance of unfamiliar applications or advertising in the status bar.

How to remove viruses:

1. Install Malwarebytes or Dr.Web Light (free versions are sufficient).
2. Run a full check (can take 30-60 minutes).
3. Remove any threats and reboot your phone.
4. If the viruses remain, reset to factory settings (instructions in the next section).

⚠️ Warning: Some viruses disguise themselves as system applications (e.g. com.android.system) If an antivirus detects a suspicious file with that name, don't manually delete it, it can knock your phone out.

6.Reset to factory settings is the last chance

If all previous methods failed, then you have to have a hard reset, which is a factory reset, which will delete all the data, but it will return the Redmi Note 9 to a clean state.

How to reset:

1. Create a backup copy of important data (contacts, photos, messages).
2. Go to Settings → About the phone → Reset settings.
3. Choose to erase all data and confirm the action.
4. Wait for the process to complete (5-10 minutes) and set your phone up as new.

If the phone is not turned on or got stuck on the Mi logo, use Recovery mode:

1. Turn off the phone (squeeze the power for 10 seconds).
2. Press Volume Up + Power before the menu appears.
3. Select Wipe Data → Wipe All Data (control – volume buttons, confirmation – Power).
4. After reset, select Reboot → Reboot to System.

💡

Resetting to factory settings deletes all data, including Google and Mi Account accounts. If you forget your Xiaomi account password, after resetting, your phone may need to enter it to unlock!

7. Hardware malfunctions - when you need to carry in the service

If the software methods didn't help, the problem could be the hardware.Typical hardware faults of the Redmi Note 9:

If you suspect a hardware breakdown:

• 🛠️ Don’t take your phone apart – you risk damaging the fees.
• 🔍 Check if the warranty is valid (even if the phone was purchased 3-4 years ago, some service centers are ready to meet the requirements of the warranty).
• 💰 Compare the cost of repairs to the cost of a new phone, for example, replacing the motherboard with a Redmi Note 9 in 2026 could cost 70-80% of the price of the new Redmi Note 12.

Where to look for a service center:

• Xiaomi’s official centers – check out the website mi.com/ru/service.
• Unofficial workshops – read reviews on Yandex.Maps or 2GIS.
• Self-repair – only if you have the experience and tools (e.g., iFixit opening kit).

FAQ: Answers to Frequent Questions