How to accurately check the battery status on Xiaomi Mi 9T: from engineering code to stress tests

Xiaomi Mi 9T (also known as the Redmi K20 in some regions) – smartphone with battery capacity 4000 mAh, but it inevitably gets worse over time, so if you notice that the device is discharged faster than usual, overheats when charging, or suddenly turns off when you're in charge. 20-30% It's time to diagnose the battery. 5 proven ways to assess its condition: from hidden menus to professional applications, as well as unique wear standards specifically for the Mi model 9T.

It's important to understand that battery status is not just a percentage of wear, but also parameters like internal resistance, discharge rate under load and temperature stability. We'll look at how to measure each of them without special equipment using only a smartphone and free tools. And at the end of the article, we'll see an FAQ that answers to frequent user errors (for example, why ##4636## doesn't show battery data on some firmware).

1. Verification through the engineering menu: secret code and hidden data

The fastest way to get technical information about the battery is to use the service code. The Mi 9T runs a universal combination for Android devices:

##4636##

After you enter, the Testing menu will open, where you will select Battery information.

• 🔋 Level - current charge in percentage (may differ from the one displayed on the screen due to calibration).
• 🔌 Voltage is a voltage in millivolts. Normal for Mi. 9T: 3700–4350 mV (below 3,500 mV critical discharge).
• 🌡️ Temperature: Battery temperature: 25-40°C. Exceeding 45°C when charging - a sign of wear.
• 📊 Health - state (not displayed on all firmware). GOOD — wear less than 20%, FAIR — 20–50%, POOR — 50%.

⚠️ Note: On custom firmware (e.g. LineageOS), the engineering menu may be disabled, in which case use alternative methods from the following sections.

2. Diagnostic applications: AccuBattery vs AIDA64

Third-party utilities provide more detailed information than standard MIUI tools, and we tested two of the most accurate applications:

AccuBattery (Play Market)

A specialised battery monitoring tool with unique features:

• 📉 Charts of discharge – shows how fast the charge drops under different scenarios (screen, games, waiting).
• 🔄 Charging cycles - counts full cycles (1 cycle) = 100% discharge + For Mi, for the Mi. 9T Battery life is designed for 500-800 cycles.
• ⚡ Charging speed -- measures current in real time. Normal for fast charging Mi 9T: 15-18 W.

How to use:

1. Install the app and give you access to battery statistics.
2. Charge your phone to 100% and wait for the calibration (1-2 cycles).
3. Check the Health tab – it will show the real capacity (for example, 3700 mAh instead of the declared 4000 mAh).

AIDA64 (Play Market)

A universal iron diagnostics utility, to test the battery:

1. Open the Battery tab.
2. Note the fields: Capacity is the current capacity (compare with the passport 4,000 mAh); Wear level is the wear rate as a percentage; Critical is the value above 40%; Technology is the type of battery (should be Li-polymer).

⚠️ Attention: AIDA64 It can show a low capacity immediately after installation. Wait for 2-3 full charge/discharge cycles for accuracy.

3. Load test: how to detect "slack" voltage

Even if the battery is at rest, it can sag under load, and this is manifested by sudden shutdowns at 20 to 30 percent charge, to check:

1. Charge the phone to 100%.
2. Install the app CPU Throttling Test (Play Market).
3. Run the test at maximum load (select the Stress test option).
4. Watch the voltage schedule in AccuBattery or the engineering menu.

How to check:

1. Put the phone down on the table with the screen.
2. Carefully press the center of the back cover, and if it bends or comes back with resistance, the battery is swollen.
3. Check if the phone rotates around its axis (put it on the table and push it slightly).The normal Mi 9T will lie flat.

⚠️ Attention: A bloated battery is a fire hazard. Don't try to puncture or bend it:

1. Turn off the phone.
2. Extract. SIM-map (if possible).
3. Contact the service center for a replacement.

5.Battery calibration: why the phone shows the wrong percentage

Over time, the Mi 9T charge controller may not display the percentage correctly (e.g., jumps from 50% to 20% per minute), due to the discrepancy between the actual capacity and the data in the firmware, to reset the statistics:

1. Discharge the phone before automatically shutting down.
2. Connect the original RAM and charge up to 100% without interruption (don’t turn on the phone!).
3. After full charging, keep charging for another 1-2 hours.
4. Turn on the phone and check the indicator.

If the problem persists:

• 🔄 Reset settings through Settings → System system → Resetting settings → Resetting battery settings.
• 📱 Update the firmware to the latest version (in new versions) MIUI improved calibration).

⚠️ Attention: Calibration won't restore battery capacity -- it only corrects percentage display. If real wear is greater than 30%, a replacement is required.

💡

Calibration only helps with software failures. If the battery is physically worn out (bloating, low voltage), calibration is useless.

When to change the battery: criteria for Xiaomi Mi 9T

The manufacturer claims that the Mi 9T battery retains 80% of its capacity after 500 charging cycles, but in practice this is dependent on the operating conditions, and replacement should be considered for the following symptoms:

Replacement cost: The original battery for the Mi 9T (article MBJ404740) costs 1500-2500 rubles depending on the region. In Xiaomi service centers, the replacement will cost 2500-3500 rubles (with work).

• 🔧 Glue - the original battery is glued, you will need a hair dryer to soften.
• 🔌 Train - Do not damage it when disconnected.
• 📄 Calibration – after replacement, perform the procedure from Section 5.

⚠️ Warning: When buying a battery, check for a protection controller (a small charge on the battery). Cheap analogues without a controller can fail in 2-3 months.

FAQ: Answers to Frequent Questions