Why Xiaomi Redmi Note 9 began to discharge quickly: a full analysis of the causes and solutions

Owners of Xiaomi Redmi Note 9 often face a problem: the smartphone, which used to hold a charge for a day, now discharges in a few hours, and the problem occurs suddenly — without falls, moisture or other obvious reasons. What is it?

Launched in 2020, this model has a 5020 mAh battery, one of the most spacious in its segment, which, in theory, should last 1.5-2 days on a single charge when used in moderation, but in practice, users note that after 1-2 years of operation, autonomy drops by 2-3 times, due to a set of factors from natural battery wear to hidden software errors.

In this article, we’ll look at all the possible causes of the Redmi Note 9’s rapid discharge, including those that aren’t covered in the standard instructions, such as the effects of non-original chargers on the power controller or hidden processes run by pre-installed Xiaomi apps.

1. Natural battery wear: when it's time to change the battery

The Lithium Polymer batteries in the Redmi Note 9 have a limited lifespan of about 500 to 800 full charge cycles, and then the capacity starts to decline steadily, and if your smartphone has been in service for more than 1.5 to 2 years, the problem is probably here.

How to check the wear of the battery without disassembling the phone?

• 🔋 Type in the phone app code ##4636##, go to Battery Information. Health should show "Good." If it's Unknown or below 80%, the battery is worn out.
• 📊 Use apps like AccuBattery (available on Google Play) to show the actual battery capacity, for example, if you're looking at 3,500mAh instead of 5020mAh, you should think about replacing it.
• ⚡ Pay attention to the charging speed: the worn-out battery charges faster (for example, up to 100% in 1 hour instead of 1.5-2 hours), but also discharges faster.

The average battery life of the Redmi Note 9 is 2-3 years with heavy use. If the phone was used in extreme conditions (constant charging from powerful adapters, overheating, discharge to 0%), the resource is reduced to 1.5 years.

⚠️ Warning: Don't trust diagnostics with ##4636## if your phone is rooted or stitched with custom firmware.

Programming errors and background processes: who “steals” the charge

Even a new battery will run out quickly if the operating system or apps are not working properly.

• 🤖 Mistakes. MIUI. Some versions of the firmware (especially) MIUI 12.5 and MIUI 13) contain bugs that cause the system to not optimize its energy consumption, for example, the mediaserver process can consume up to 20% charge per hour.
• 📱 Xiaomi services (Mi Cloud, GetApps, Mi Video) often run in the background, even if you do not use them.
• 🔄 Auto Updates: Auto-Update Apps via Google Play or Mi App Store may be triggered at the wrong time.
• 🕵️ If the phone starts to run out suddenly, check the list of installed programs for suspicious ones (for example, with administrator rights).

How to find “gluttonous” processes?

1. Go to Settings → Battery and Performance → Battery Use.
2. Click on the graph and select CPU Use. This shows the processes that are active in the background.
3. If an app consumes more than 10% of its charge for no apparent reason, remove or limit its operation.

Pay special attention to system processes called android.system, kernel or qti. Their high activity may indicate hardware problems (for example, a malfunction of the communication module).

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If Android System is the leader in the battery consumption list, try turning off the Adaptive Battery feature in the settings, which sometimes works incorrectly and, instead of saving, increases consumption.

3. Non-original chargers and cables: a hidden threat

Many users don't care what charger they use, but the Redmi Note 9 is sensitive to power quality, and using cheap or uncertified adapters results in:

• ⚡ Unstable voltage that damages the power controller and accelerates battery wear.
• 🔥 Battery overheating during charging (especially if the phone is used in parallel).
• 📉 Incorrectly defined charge level – the phone can show 100%, but in fact it is only charged at 80%.

How to check the compatibility of the charger?

If you lose the original charger, choose Quick Charge-enabled adapters. 3.0/4.0 or Power Delivery (PD). From budget options suitable models from Baseus, Anker or Xiaomi (series Mi Charge Turbo).

⚠️ Warning: If after connecting a non-original charger, the phone begins to warm up or turn off when charging, immediately stop using such an adapter.

4. Network and communication settings: how 4G/5G Wi-Fi affects the battery

Redmi Note 9 supports network support 4G LTE And Wi-Fi 5, but if you set them up incorrectly, you can significantly reduce the time you're going to run:

• 📶 If the cellular signal is weak (1-2 divisions), the phone spends a lot of energy on amplifying it.
• 🔄 Automatic switching between 2G/3G/4G. This feature is useful for saving traffic, but increases the load on the modem.
• 📡 Wi-Fi and Bluetooth in the background. Even if you're not using them actively, the modules continue to scan the airwaves.
• 📍 Geolocation and GPS. Applications like Google Maps or Yandex.Navigator can include GPS without your knowledge.

How to optimize network settings?

1. Go to Settings. → SIM-maps and mobile networks, and disable "Network Search" Manually select the operator with the best signal.
2. In the Settings section → Wi-Fi disable the function “Connect to open networks automatically».
3. B Settings → Location: Set Device Only (without network data).
4. If you don't use it. 5G (Redmi Note 9 does not have it, but is in Note 9 Pro, disable the search for new generation networks in the modem settings.

Also check if the Mobile Hotspot or Wi-Fi hotspot mode is on in the background, and these features drain the battery in 2-3 hours, even without the connected devices.

Shut down search network|Select a regime 2G/3G low-signal 4G|Disable Wi-Fi and Bluetooth when not in use|Check geolocation in applications|Use the “On the Plane” mode at night-->

5.Screen and brightness: hidden settings that eat up the battery

Redmi Note Display 9 permittingly 2340×1080 diagonally 6.53 It's one of the major energy consumers, and even at its minimum brightness, it can consume up to a few hours. 30–40% The problem is compounded by the fact that:

• 🌞 Automatic brightness with light sensor is used (it often works incorrectly).
• 🎨 The mode “Saturated colors” or “Reading” is enabled (increase the load on the GPU).
• ⏳ Setting too long "Switch off delay" (more than 30 seconds).
• 🔄 The frequency of the screen update is increased (in Redmi Note 9 it is fixed - 60 Hz, but some firmware allows you to accelerate it to 90 Hz, which greatly puts the battery down).

How to set up the screen to save charge?

1. Go to Settings. → Display and set the brightness to 30-50% manually».
2. In the Settings section → Display. → Select the “Standard” mode instead of “Saturated».
3. Reduce the screen shutdown time to 15-20 seconds.
4. Turn off “Always-on Display” (if it was activated through hidden settings).

If you are using Redmi Note 9 Pro AMOLED-So if you use a screen, you turn on a dark theme, which reduces battery consumption by 10 to 15 percent. IPS-matrix.

6.Temperature conditions: why the phone discharges in the cold or in the heat

Xiaomi Redmi Note 9 is designed to work in the temperature range from 0°C to 35°C. When you go beyond that, the battery loses capacity or shuts down:

• ❄️ Cold (below 0)°C) Lithium polymer batteries lose up to 50% of their capacity at low temperatures, and the phone can show 30% of its charge and shut down immediately.
• 🔥 Heat (above 35)°C) Overheating accelerates battery degradation if the phone heats up above 40°C, the controller forcibly disables charging.
• ☀️ Direct sunlight. Even at room temperature, the heating of the housing under the sun can exceed the permissible limits.

How to protect your phone from temperature effects?

• 🧤 In winter, carry your smartphone in your inner pocket, not in your bag or backpack.
• 🚗 In summer, don't leave it on the torpedo of the car. Use holders with ventilation.
• 🔋 Do not charge your phone at temperatures below 5.°C or higher than 30°C.
• 📴 If the phone overheats, turn it off and let it cool to room temperature before charging.

If the Redmi Note 9 suddenly turns off in the cold, but after heating up in the hands, the problem is in the battery, in which case only replacing the battery with a new one will help.

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Lithium polymer batteries are irreversibly losing capacity in extreme temperatures, and if you use your phone frequently in the cold or in the heat, you may need to change the battery in 1 to 1.5 years.

7 Viruses, Mining and Malware: How to Detect Them

If the phone starts to run out suddenly, for no apparent reason, a virus attack is possible.

• 💻 Mining cryptocurrency in the background (CP consumption up to 100%, strong heating).
• 📤 Send. SMS to pay numbers or download data on the Internet.
• 🔍 Monitor your actions (keyloggers, spies).

Signs of infection:

• The phone is warming up without load.
• In the list of battery consumption, unknown processes lead (for example, com.android.system with unusual PID).
• Mobile traffic consumption has increased.
• Unknown apps or advertisements appear.

How to check and remove viruses?

1. Install antivirus (Dr.Web, Kaspersky Mobile, Malwarebytes) and scan the system.
2. Check the list of installed applications in Settings → Remove suspicious applications (especially with administrator rights).
3. Disable the installation of applications from unknown sources (Settings) → Confidentiality).
4. If the virus is not removed, reset to factory settings (Settings → About Phone → Reset settings).

⚠️ Warning: Some viruses disguise themselves as system applications (e.g. Google Play Services) If antivirus finds a threat in such files, do not manually delete them - this can lead to loss of the phone's performance.

8 Hardware malfunctions: when repairs are not necessary

If all software methods have been tried, but the phone still discharges quickly, the problem may lie in the hardware.

• 🔌 Symptoms: phone not charging from original RAM, wrong percentage of charge, spontaneously shuts down.
• 📶 A damaged communication module, if a smartphone is not catching the network or Wi-Fi well, it spends a lot of energy amplifying the signal.
• 🔋 Battery bloating. Signs: phone body deformed, screen raised, battery quickly discharges even when it's off.
• 🔧 Oxidation of contacts on the board (due to moisture or condensation) This leads to unstable nutrition of components.

How to diagnose hardware problems?

If you suspect a hardware malfunction, don't try to repair the phone yourself.The Xiaomi Redmi Note 9 has a complex design with adhesive battery mounting - unqualified intervention can damage the plumes or display.

The cost of replacing the battery in the service center is about 1500-2500 rubles (depending on the region), the power controller or the repair of the board will cost more - from 3000 rubles.

FAQ: Frequent questions about the Redmi Note fast discharge 9