Why the battery is quickly discharged on Xiaomi Redmi Note 9: full parsing + 12 ways to fix

Xiaomi Redmi Note 9 when released in 2020 was famous for a record for the budget battery capacity — 5020 mAh. But after 2-3 years of active use, many owners are faced with the fact that the smartphone discharges in half a day, or even faster. And the problem arises even with minimal load: messengers in the background, rare calls, turned off mobile Internet.

We analyzed 12 key causes of the Redmi Note 9’s rapid discharge, from the banal wear of the battery to hidden MIUI firmware errors. The article does not contain general tips like “turn off Bluetooth” (it will not work), instead, specific instructions with step-by-step actions, diagnostic codes and data from service centers, and you will learn when the problem is solved software and when it is time to carry the phone for repair.

Spoiler: 80 percent of the time, it's not the battery itself, it's the software or the settings that are wrong, but the good news is that most of the causes can be fixed on their own in 10-30 minutes.

Battery wear: how to check the real capacity

Redmi Note 9 Lithium Polymer batteries are designed for 500-800 full charge cycles. After that, the capacity begins to fall steadily. If your smartphone is older than 2 years and discharges in 3-4 hours in normal use, first check the wear and tear.

This can be done without disassembling the phone - through the service code or third-party applications:

• 📱 Enter the dialer: ##4636## → Select Battery Information. Compare Level (current charge) and Health status. If the latter is below 80%, the battery is critically worn out.
• 🔋 Install the AccuBattery app (free on Google Play). 2-3 In the charging cycles, it shows the actual capacity in mAh. 5020 You see. 3500 MACh - Time to change battery.
• 🔧 V MIUI Go to Settings. → Battery → Battery status: This shows approximate wear (but often understated).

⚠️ Warning: If the capacity has fallen below 70% of the original, no calibration or reset will help.The only solution is to replace the battery. ~1 500–2 000 ₽ (Non-original analogues are cheaper, but their capacity is often overstated and their service life is lower.

2.App background activity: Who is "eating" the charge?

MIUI is known for aggressive background optimization, but some applications are able to bypass limitations.

• 📸 TikTok, Instagram, YouTube – even in the folded state they can consume up to 15-20% Charge per hour due to autoplaying video.
• 🎮 Games (PUBG Mobile, Genshin Impact – leave background processes for ‘fast start’ that load the processor.
• 📊 Fitness apps (Mi Fit, Google Fit) – constantly monitor sensors (stepmeter, pulse), even when the screen is turned off.
• 🔄 Auto-update apps in Google Play – can be launched every time 2-3 hour.

How to find and disable “gluttonous” applications:

1. Go to Settings → Battery → Battery Use.
2. Click on the three dots in the upper right corner → Show the use of the system.
3. Sort the list by Total Consumption. Apps with a consumption of >5% in the last 24 hours are suspicious.
4. For each such application: Open its settings → Permissions → Turn off Autostart and Background Activity. In Settings → Applications → Application Management, select the application → Limit background activity.

💡

If you don't use Facebook or VK, delete them altogether and use the web version through your browser. App-based social media is one of the biggest killers of the battery.

3. MIUI firmware bugs: bugs that steal charge

The Redmi Note 9 received the latest major update to MIUI 13 based on Android 12, but even it contains bugs that affect autonomy.

⚠️ Note: If after the update MIUI autonomy fell on 30-40%, Try to go back to the previous version:

1. Download the firmware from en.miui.com (select Stable for Redmi Note 9, encoding merlin).
2. Go to Settings → About Phone → MIUI → Press 10 times on the MIUI version to turn on Developer Mode.
3. Return to Settings → Additional → For Developers → Enable USB Debugging and OEM Unlocking.
4. Connect your phone to your PC, use the Mi Flash Tool for firmware.

For diagnosis:

1. Check the temperature of the processor through AIDA64 (Sensors section) Normal: up to 40°C in plain, up to 60°C under load, if higher, you need to replace the thermal paste.
2. Run a battery test in AccuBattery. If the voltage at 100% charge is greater than 4.35V, the power controller is faulty.
3. Light a flashlight on the screen at an angle, and if you see waves or swelling, the battery is swelling.

⚠️ Warning: If the battery is swollen, immediately turn off the phone and do not use it until the battery is replaced!

💡

You can't squeeze a bloated battery or fix it, and the only solution is to replace it at a service center, and the average cost of work is 1,500 to 2,500. ₽ (2026).

7.Optimize MIUI for maximum autonomy

If the battery is fine but the battery is still not comfortable, try deep optimization, which will reduce the charge consumption by 15-25%.

1. Turn off animation: Enable Developer Mode (see Section 3). Go to For Developers → Set Windows Animation Scale, Transition Animation Scale, and Off-Duration Scale of Animator Duration.
2. Switch to dark theme: In Settings → Screen → Dark theme, select Always On. For applications that don’t support dark mode, use Forced Dark Theme to be included in Special Options.
3. Limit background data transfer: C Settings → SIM-maps and mobile networks → Transfer data, turn off Background data. For individual applications: Settings → Annexes → Application management → [select the application] → Data data → Background data transmission.

Set up the battery mode:

• In Settings → Battery → Battery mode, select Charge Saving or Balanced.
• Activate Supercharge Savings at levels below 15%.

💡 A useful tip: if you rarely use NFC, IR-port(s) or FM-radio, turn them off in settings. These modules consume power even when they're off.

8.When is it time to carry the phone for repair?

If you’ve tried all of these, but the Redmi Note 9 still runs out in 2-3 hours, it’s probably a hardware problem.

• 🔋 The battery swelled or deformed the body.
• 🔥 The phone overheats to a simple (above 45)°C).
• ⚡ Charging is jerky or does not go at all.
• 📉 Battery capacity by AccuBattery below 60%.
• 🔌 The phone turns off when 20-30% charge.

Average repair prices (2026, Moscow):

⚠️ Warning: Don't trust battery replacement to garage-makers! a poor battery can:

• It's 2-3 months.
• Do not keep the declared capacity (for example, instead of 5020 mAh will be 3000 mAh).
• Short-circuit and burn the fee.

Always require a warranty for work and parts (at least 6 months).

FAQ: Frequent questions about the Redmi Note battery 9