Why is the Mi 9T battery running down faster than before?
Smartphone Xiaomi Mi 9T (also known as Redmi K20 in some regions) was released in 2019 with a battery capacity of 4000 mAh. Even after 3-4 years of active use, many users are faced with the fact that the battery holds a charge of only a few hours - instead of the declared day. The reason is not always the "aging" of lithium-ion cells: often to blame background processes, unoptimized applications or software failures in MIUI.
Before you run to the service center, you should check the battery status yourself. In this article, 5 working diagnostic methods are used: from hidden engineering menus to third-party utilities with detailed statistics. You will learn how to find out the real battery capacity in mAh (rather than the percentage of wear), the number of charging cycles and even the temperature of the cells under load. All methods are tested on the Mi 9T with MIUI 12-14 and do not require root rights.
Method 1: Code #4636## - Basic information about the battery
The fastest way to get battery data is to use the Android hidden menu, which is available on all Xiaomi smartphones, including the Mi 9T, and does not require the installation of additional apps.
Instructions:
- 📱 Open the "Phone" application (standard dialer).
- 🔢 Enter the combination: ##4636## (without spaces).
- 🔋 In the menu that opens, select the tab "Battery Information".
Here you'll see:
- 🔋 Charge level (in percent and millivolts).
- 🌡️ Battery temperature (normal: 25–40)°C on charging, up to 45°C under load).
- ⚡ Power supply (e.g., usb or ac when connected to a charger).
⚠️ Warning: If the battery temperature exceeds 50°C in standby mode (no games or charging), this is a sign of critical wear or malfunction of the controller.
Turn off the charger and let cool for 30 minutes|Close all background applications|Check for swelling (carefully probe the back cover)|Reset to factory settings if the problem persists-->
Method 2: AccuBattery Appendix - detailed statistics
AccuBattery (from developer Digibites) is one of the few apps that shows real battery capacity per mAh, rather than an abstract "health percentage." For the Mi 9T, this is especially important, as regular MIUI tools often understate data.
How to use:
- Download AccuBattery from Google Play.
- Charge your smartphone to 100% and leave it on standby for 1-2 hours (to stabilize readings).
- Open the app and go to the Health tab.
- Notice the "Estimated capacity" parameter. Compare it to the factory's 4,000 mAh.
| Capacity index | Battery status | Recommendations |
|---|---|---|
| 3600–4,000 mAh | ✅ Excellent. | Continue to use as usual |
| 3000–3599 mAh | ⚠️ Average (wear and tear 10–25%) | Watch the temperature, avoid deep discharges |
| 2500-2999 mAh | ⚠️⚠️ Critical (wear 25-35%) | Consider replacing your battery in the next 3-6 months |
| < 2,500 mAh | ❌ Emergency (wear and tear) >35%) | Immediate replacement! Risk of sudden shutdown and bloating |
AccuBattery also shows:
- 📊 Time-discharge schedule (useful for identifying "gluttonous" applications).
- 🔄 Number of charging cycles (norm for lithium-ion batteries up to 500 cycles).
- ⚡ Charging/discharge speed in mA (e.g., fast charging Mi) 9T should show 1800-2200 m).
Once a month | Once every 3 months | Only when problems start |Never calibrated-->
Method 3: MTK Engineering Menu (#36446337##)
The Xiaomi Mi 9T is built on a Qualcomm Snapdragon 730 processor, but some firmware features a MediaTek engineering menu (the remnant of test builds) that provides advanced battery data, including the voltage of each element and the resistance of the circuit.
How to open it:
- Enter the dialer: ##36446337##.
- Go to the Battery Information section.
- Note the parameters: Battery Voltage (normal: 3.7-4.2 V at 100% charge), Battery Temperature (in degrees Celsius), Battery Health (can show Good, Normal or Bad).
⚠️ Warning: If the Battery Health menu has Bad and the voltage at 100% charge is below 4.0V, this means irreversible degradation of the elements.
What to do if the engineering menu is not opened?
Method 4: ADB-Teams for Advanced Users
If you want accurate data from the charging controller, you can use ADB (Android Debug Bridge), which is suitable for those who are ready to work with the command line.
Instructions:
- Install. ADB-PC drivers.
- Enable Developer Mode on Mi 9T: Go to Settings → About Phone. 7 times click on MIUI Version. Return to Settings → Additional → For Developers and enable USB Debugging.
adb shell
dumpsys batteryIn conclusion, pay attention to the lines:
- Level: 85 is the current charge in percentage.
- Voltage: 3987 - voltage in millivolts (3987 mV = 3.987 V).
- temperature: 305 - temperature in tenths of a degree (305 = 30.5 ° C).
- Health: 2 - Battery status (2 = Good, 3 = Overheat, 4 = Dead).
💡
If the ADB output has the line technology: Li-poly, it confirms that your Mi 9T has an original lithium-polymer battery. Counterfeiters often use cheap Li-ion cells with less resource.
Method 5: Visual examination and bloating test
Even if software tests show a "normal" condition, the physical wear of the battery can be critical, and battery bloating is one of the most dangerous malfunctions, as it can rupture the case or cause fire.
How to check:
- 🔍 Put your smartphone on a flat surface (screen up), and if it sways like a boat, the battery swells.
- 🖐️ Carefully swipe your finger between the screen and the body.
- 🔋 Put a flashlight on the back cover, and if you see a bubble under the plastic, the battery needs to be replaced.
Additional symptoms of a bloated battery:
- 🔌 Charging is interrupted or is jerked (contacts leave due to deformation).
- 📱 The screen spontaneously "steps away" from the body when pressed.
- 🔊 Characteristic creak or crack when pressed on the back panel.
⚠️ Warning: If you find bloating, do not attempt to puncture or compress the battery! lithium polymer cells can ignite if damaged. Disable your smartphone immediately and contact a Xiaomi service center or an authorized workshop.
What to do if the battery is worn out?
If the diagnosis showed that the battery capacity fell below 2500 mAh or it swelled, there are two options:
- Official replacement at the service center: ✅ Pros: original battery, 6-12 month warranty. ❌ Cons: cost 3000-5000 ₽ (depending on the region).
Self-sustaining replacement
- ✅ Pros: cheaper (battery costs) ~1500 ₽ AliExpress).
- ❌ Cons: risk of damage to plumes, loss of tightness (dust protection) IP53 will be broken).
If you decide to change the battery yourself, follow the rules:
- 🛠️ Use plastic blades, not metal screwdrivers (the risk of puncture!).
- 🔥 Before work, discharge the battery to 25-30% (less risk of fire in accidental KZ).
- 🔧 Buy only batteries with labels. MB-J10B (original article for Mi 9T).
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Even after the battery is replaced, it needs to be calibrated: fully charge the smartphone, then discharge to 0% and recharge to 100%. Repeat the cycle 2-3 times for the controller to work accurately.