Xiaomi Redmi Note 9 Pro 128GB battery is one of the key components that determines the battery life of the smartphone. After 1.5-2 years of active use, many owners notice that the battery goes down faster, the phone suddenly turns off at 20-30% charge or overheats during charging. But how do you determine that the problem is in the battery, and not in software failure or background of running applications?
In this article, we'll look at 5 reliable ways to check, from hidden engineering menus to physical inspection of the battery after disassembly, how to find out the real capacity of the battery, assess its wear and see if it's time to think about replacing. All methods are tested on the Redmi Note 9 Pro with MIUI 12-14 firmware and work without root rights.
1. Check through the engineering menu (#4636##)
The fastest way to get basic battery information is to use the Android hidden engineering menu, which is available on all Xiaomi smartphones without installing additional apps, and the data here is displayed in real time, but has limitations: you will see the current status, but not the wear history.
To open the menu:
- 📱 Open the phone app and enter the combination: ##4636##.
- 🔋 In the window that appears, select the Battery Information tab).
- 📊 Pay attention to the parameters: Level (Level) - current percentage; Status - must be Charging or Discharging; Power source (Power source) — USB or AC when charging; Temperature - the norm is 25-40°C.
⚠️ Warning: If the battery temperature exceeds 45°C in plain or 50°C when charging is a sign of critical wear or failure of the controller.
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If the engineering menu doesn't open, try entering the code through the Calculator app: dial ==4636=== and press =. This is an alternative method on some MIUI firmware.
| Parameter | Normal value. | Critical significance |
|---|---|---|
| Temperature. | 25–40°C | >45°C (in plaintiff) |
| Tension. | 3.7–4.2 | <3.5 B or >4.3 B |
| Status. | Charging/discharging | Unknown or Mistake |
| Charge level | Corresponds to the indicator | Sharp jumps (for example, from 50% to 20%) |
2. Diagnostics through the AccuBattery application
AccuBattery is one of the most accurate applications for monitoring battery health. It analyzes charging cycles, real capacity and wear rate. For the Redmi Note 9 Pro with the original 5020 mAh battery, the app will show how much is left of the factory performance.
How to use:
- Download AccuBattery from Google Play.
- Charge your phone to 100% and leave it on charge for another 15 minutes (for calibration).
- Use your smartphone in normal mode until discharge to 20-30%.
- In the Health section, look at the Calculated Capacity parameter.
Example of decoding results:
- 🔋 90-100% of the factory capacity – battery in excellent condition.
- 🟡 80-89% - noticeable wear and tear, but no replacement is required.
- 🟠 70-79% – Autonomy decreased by 30-40%, consider replacing.
- 🔴 <70% — critical wear, the battery may suddenly shut down.
Turn off battery optimization for the application | Charge the phone to 100% and hold on charging 15 min| Discharge up to 20% without recharging | Repeat the cycle 2-3 times for accuracy | Compare the data with the wear table-->
Important: AccuBattery shows the design capacity, not the actual capacity, USB-However, for household diagnostics, the error does not exceed 5-10%.
Visual inspection of the battery (after disassembly)
If you're ready to disassemble the Redmi Note 9 Pro, a visual inspection of the battery will give you the most complete picture.
- 🔋 The phone suddenly turns off at 30-50% charge;
- 🔥 The case swelled (gaps between the screen and the frame, the bulge of the back panel);
- 🛠️ The battery is already being replaced.
You'll need to take this apart.
- 🔧 Plastic mediator or guitar mediator;
- 🔨 Cross screwdriver (usually) PH00);
- 🧲 Screen removal suction cup (optional);
- 🔥 Fryer (for softening glue).
⚠️ Warning: Disassembling your smartphone will void the warranty (if it's still valid) and could damage the plumes. If you're not sure about your skills, contact the service center. A bloated battery is dangerous, it can ignite if punctured!
What does a bloated battery look like?
What to check during the inspection:
| Sign. | What does it mean? | Recommendation |
|---|---|---|
| Bloating (even mild) | Critical wear and tear, explosion risk | Immediate replacement |
| Dark spots or stains | Electrolyte leak | Replacement + fee check |
| Oxidation of contacts | Bad contact, overheating | Alcohol cleaning or substitution |
| Scratches or punctures | Mechanical damage | Replacement is mandatory |
4. Check through ADB (for advanced users)
If you want the most accurate battery data, including the number of charging cycles and the actual voltage, you can use ADB (Android Debug Bridge), which requires connecting the phone to a computer, but gives you access to hidden parameters.
Instructions:
- Enable USB Debugging in the Developer Settings (Settings → About Phone → MIUI Version – Press 7 times, then return to Additional → For Developers).
- Connect the Redmi Note 9 Pro to your PC and confirm your trust in the device.
- Open the command line (Windows) or terminal (macOS/Linux) and type:
adb shell
dumpsys batteryIn the answer, note:
- 🔢 Capacity - Current level of charge;
- ⚡ Voltage - voltage (normal: 3.7-4.2 V);
- 🔄 charge counter - amount of charged energy (in mAh);
- 📅 Technology - battery type (should be Li-ion or LiPo).
⚠️ Note: If the health parameter shows a value COLD, OVERHEAT, DEAD or UNKNOWN — This is a direct sign of a malfunction. OVERHEAT Turn off the phone from charging immediately!
Once a month|Six months|Only when the problems start.|Never checked.-->
5. Test by means of USB-tester
USB-The tester is a compact device that connects between the charger and the phone and shows real current, voltage and power consumption. For the Redmi Note 9 Pro, this is especially useful because it allows you to use the tester:
- 🔌 Check if the charger is giving the declared 18/27/33 Watt;
- 📉 Evaluate the speed of discharge in simple and under load;
- 🔋 Identify "drawdown" of voltage at low charge (sign of wear).
How to run the test:
- Connect. USB-charger.
- Connect the tester to the phone.
- Run a resource-intensive application on Redmi Note 9 Pro (for example, a game or benchmark).
- Compare the numbers to the norm:
| Parameter | Norma (when charging) | Deviation (problem) |
|---|---|---|
| Voltage (V) | 4.8–5.2 B | <4.5 B or >5.5 B |
| Current (A) | 2.0–3.0 A (fast charging) | <1.0 A at 18+W charging |
| Power (W) | 18-27 W | <10 W when connected to the network |
| Temperature (°C) | Up to 40°C. | >45°C |
💡 Useful advice: If the tester shows current <0.5 And when charging from the original power supply, the problem may be in the connector. USB-C Try cleaning the port with compressed air or replacing the cable.
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USB-The tester is the only way to know the actual battery capacity without disassembly. If less than 4,000 mAh has passed through the tester during a discharge of 100% to 0%, the battery is worn out by more than 20 mAh%.
When is it time to change the battery?
Even if the diagnosis shows wear and tear, it doesn't always require immediate replacement. Here's a checklist for when exactly to act:
- 🔋 The phone turns off at 30% or higher (even after calibration).
- 🔥 The case swelled or there were gaps between the screen and the frame.
- ⚡ Autonomous life has decreased by 1.5-2 times compared to the new state.
- 📉 AccuBattery or ADB show capacity <3500 mAh (from the reference) 5020 mAhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh).
- 🛑 The phone overheats to a simple or refuses to charge.
The cost of replacing the battery with the Redmi Note 9 Pro 128GB in 2026:
- 🔧 Original battery (with warranty): 2500-3500 ₽;
- 🔋 Analogue (quality): 1200–2000 ₽;
- 🛠️ Work of the master: 800-1500 ₽ (If you buy a battery separately).
⚠️ Note: When replacing the battery, be sure to check that the master:
- 🔧 Used a new glue to fix the battery;
- 🔌 Checked the charging controller's operation;
- 📋 Provided a guarantee of at least 6 months.