Calibration of the battery on Xiaomi Redmi Note 9S: when you need and how to do it correctly

Why the Redmi Note 9S battery suddenly “lies” about the charge and how to fix it

Have you ever encountered a situation where the Xiaomi Redmi Note 9S shows 30% charge and then suddenly shuts down after 5 minutes? Or vice versa - the phone hangs 1% for hours until it finally runs out? These are classic symptoms of a battery controller desynchronizing with a real charge level. The reason is not the physical wear of the battery (although it also affects), but the failure of the software that is responsible for monitoring energy.

Battery calibration is the process of matching the power controller data (the chip built into the battery) with the actual capacity. On the Redmi Note 9S with its 5020 mAh battery, this procedure is especially relevant after a year of use, when charging cycles accumulate errors. But it is important to understand that calibration will not restore worn-out battery cells, but only return accurate charge readings.

This article is the only proven calibration method for the Redmi Note 9S, approved by Xiaomi service centers in 2026, and also analyzes myths (for example, about “three full cycles”) and typical errors that exacerbate the problem.

When you really need calibration: 5 clear signs

Don't be too quick to calibrate the battery at the slightest suspicion, but here are the specific symptoms that signal the need for the procedure:

• 🔋 The phone turns off at readings of 15-30% of the charge, although previously worked up to 1-5%.
• 📉 The percentage of charge “jumps”: for example, from 45% immediately to 20% after rebooting.
• ⚡ After charging, the indicator shows 0%, and after a second - 50%.
• 🕒 Phone gets stuck at one percent (usually 1% or 100%) for more than 20 minutes.
• 🔄 Battery monitoring applications (e.g. AccuBattery) show a discrepancy of more than 10 percent from system data%.

If you know any of these, you can start calibrating them, but first, check for alternative reasons.

• 🔌 Faulty charger: Try Xiaomi's original 18W power supply.
• 📱 Background Processes: Open Settings → Battery → Using the battery and check if any app is eating the charge.
• 🔄 Firmware failure: Update MIUI The latest version sometimes solves the problem without calibration.

⚠️ Warning: If the phone turns off at 50% charge and no longer turns on without recharging, the problem is not calibration, but critical battery wear (capacity dropped below 60.

Calibration Preparation: What to Do in Advance

Calibration is not just about "discharge and charge." Incorrect preparation can lead to accelerated battery wear or even a controller failure.

Disable battery optimization for system applications |

Remove the cover (overheating distorts the results)|

Close all background applications |

Connect the original USB-C| cable

Choose a time when the phone will not need 6-8 hours-->

Now, more details on each item:

1. Turn off battery optimization for system processes. Go to Settings → Applications → Application Management → Three dots (menu) → Special access → Battery Optimization. Find MIUI System and Android System, select No Limits.
2. Temperature: The ideal temperature for calibration is 15–25°C. If the phone overheats above 30°C, the process will have to be interrupted.
3. Use the original charging. The 18W power supply (the MDY-11-ES model) provides a stable current, which is critical for accurate calibration.

⚠️ Warning: If you use wireless charging or power bank, the calibration will be inaccurate due to voltage fluctuations.

We also recommend that you install the AccuBattery app (available on Google Play) to monitor the actual capacity before and after the procedure, which will help you evaluate the effectiveness of the calibration.

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Before calibrating, back up your data via Settings → System & Device → Backup. In rare cases, a controller reset may result in unsaved files being lost.

Step-by-step: how to calibrate the battery on the Redmi Note 9S

There are two calibration methods: software (through the recovery menu) and manual (charging-discharge cycles). For the Redmi Note 9S, it is more effective to combine both approaches. Let's start with the software method, since it resets the controller data.

Step 1: Reset battery data via Recovery Mode

1. Turn off the phone.
2. Press the Power + Volume buttons up for 10-15 seconds at the same time until the Mi logo and Recovery menu appear.
3. Use volume buttons to navigate and select Wipe & Reset.
4. Then select Wipe Battery Stats (on some versions of MIUI, this item may be called Battery Calibration).
5. Confirm the action and restart the phone.

This step resets the controller's statistics, but it doesn't calibrate the battery completely.

Step 2: Complete discharge-charging cycle

Warning: this phase will take 6-8 hours. Don't interrupt the process.

1. Discharge your phone before it turns off. Use it as normal (games, videos) until it shuts down on its own.
2. Don't turn it on right away! Leave the phone off for 30 to 60 minutes, to stabilize the voltage.
3. Charge to 100% with the original charger. Do not interrupt the process even if the phone is heated (but make sure the temperature does not exceed 35 ° C).
4. Keep charging for another 2 hours after reaching 100%, which is called "recharging" and is necessary to align the battery cells.
5. Turn off the charger and turn on the phone immediately. If the charge percentage is less than 100%, repeat steps 3-4.

After this cycle, the battery controller should be synchronized with the real capacity. To consolidate the result, it is recommended to repeat the cycle 1 more time in 2-3 days.

Typical calibration errors and how to avoid them

Many users wonder why the problem comes back after a week after calibration, and 90 percent of the time, these errors are to blame:

Another common mistake is frequent calibration, which is to do it every 3 to 6 months or when symptoms appear, and frequent resets of the controller can, on the contrary, destabilize its operation.

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Calibration doesn't increase the actual battery capacity -- it only corrects the controller readings. If the phone runs out in 3-4 hours, the problem is battery wear, not software failure.

What to do if calibration does not help

If after 2-3 calibration cycles the problem persists, check these points:

• 🔍 Battery diagnostics: type in dial ##4636##, select Battery Information. If the charge level and voltage are far from the actual values, the controller is damaged.
• 📊 Wear check: in AccuBattery, look at Battery Health. If it's below 70%, calibration is pointless, you need a new battery.
• 🔄 Reset to factory settings: sometimes failures in the MIUI They distort the battery data. Make a backup and reset to Settings. → The phone. → Resetting settings.

If none of the methods worked, contact the service center. 9S Often the power controller (microchip) fails BQ25890), The average cost of repair in 2026 is 1500-2500. ₽.

⚠️ Warning: Don't try to replace the battery controller yourself! on the Redmi Note 9S It is integrated into the battery and any intervention without specialized equipment can cause a fire.

How to extend the life of the battery after calibration: 7 rules

Calibration will return accurate charge readings, but to prevent the problem from returning, follow these recommendations:

• 🔌 Avoid deep discharge (below 10%) and full charge (above 90%.
• 🌡️ Do not use your phone in the cold (below 0)°C) or in heat (above 35)°C).
• 📵 Turn off Wi-Fi, Bluetooth and GPS, Background processes eat up to 15 percent of the charge a day.
• 🔄 Update. MIUI Up to the latest version – in the new firmware optimized algorithms power management.
• 🚫 Don't use "charging accelerators" and apps to "battery optimization": They often conflict with the controller.
• 🛌 Charge your phone overnight? use smart charging (in the MIUI There is an optimised charging function that stops the process by 80%).
• 📊 Check your battery health once a month with AccuBattery or code #4636##.

Compliance with these rules will increase battery life by 20-30% and delay the next calibration.

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If you play heavy games often (like Genshin Impact or Call of Duty Mobile), turn on performance mode in Settings → Battery → Modes. This will reduce FPS drawdowns, but increase charge consumption by 25-30%.

FAQ: Answers to Frequent Questions About Redmi Note 9S Calibration