Xiaomi Mi 9T (aka Redmi K20 in the global version) is one of the most popular smartphones of the brand, but even its battery of 4000 mAh is not eternal. After 2-3 years of active use, the battery capacity can fall by 20-30%, leading to rapid discharge, sudden shutdowns and overheating. In this article, we will examine all the available methods of checking the state of the battery, from standard MIUI tools to engineering codes and third-party applications.
It's important to understand that the Mi 9T has a lithium polymer battery that degrades even when properly operated, but some factors accelerate wear: frequent charging to 100%, use of unoriginal RAM, overheating or deep discharge. Before you run to the service center, try to diagnose the problem yourself - this will save time and money.
We tested all methods on the Mi 9T with MIUI 12-14 and Android 10-12. If your smartphone runs on older firmware, some menu items may differ, we will warn you about this separately.
1. Check through the standard MIUI menu: what the system shows
The easiest way is to look at the battery settings, and here you'll see usage statistics, but not the exact wear rate, but this data will help you identify anomalies.
Open Settings → Battery and Performance → Battery Use. Pay attention to:
- 📊 Discharge schedule – if a smartphone loses 10-15% per hour in standby mode, this is a signal of problems.
- ⚡ Screen time – with a normal Mi battery 9T Must have 5-6 hours of active use.
- 🔥 Temperature – if the battery is heated above 40°C no load, it's critical.
This menu also has a Battery Status section (which is hidden on some firmware) and if it is available, it will show approximate wear in the format of Good, Medium or Bad. Unfortunately, MIUI does not display accurate capacity figures - this requires other methods.
⚠️ Note: If you see the Android System app or MIUI with abnormal consumption (more than 20% per hour), this may indicate not battery wear, but software failure.
2 Hidden engineering codes: how to find out the real capacity
MIUI hides detailed information about the battery, but it can be extracted through service codes, which run on most Xiaomi smartphones, including the Mi 9T.
Open the phone application and enter:
##4636##You will be taken to the Testing menu. Select Battery Information and note:
- 🔋 Level of charge (level) - current percentage.
- 🔌 Voltage – the norm for Mi 9T 3.7-4.2 V. If below 3.5 V, the battery is deeply discharged.
- 🌡️ Temperature (optimal 25-35)°C. Above 45°C dangerously!
- 📏 Max. capacity (Scale) – if the value is below 80%, the battery is worn out.
Another useful code:
##284##It runs a battery test that shows the actual capacity in mAh (like 3200 instead of 4,000), and compare that to a passport value of 4,000 mAh, which is the difference in wear.
What do I do if the codes don't work?
3. Diagnostic applications: AccuBattery, CPU-Z and others
Standard MIUI tools provide limited information, so it's better to use third-party tools to diagnose accurately. We tested 5 popular apps and selected the most reliable ones.
| Annex | What shows | Pluses | Cons |
|---|---|---|---|
| AccuBattery | Capacity, wear, temperature, charging cycles | The most accurate, works without root | You need to calibrate 2-3 cycles. |
| CPU-Z | Stress, temperature, condition. | Quick analysis, no calibration. | Less accurate wear |
| Battery Guru | Capacity, working time, savings tips | Simple interface | Advertising, paid functions |
AccuBattery is a device that not only shows current wear and tear, but also analyzes battery health based on charging cycles.
- Charge your smartphone to 100% and calibrate the app.
- Use your phone as usual for 2-3 days.
- Check the Health section - there will be an exact percentage of wear and tear.
⚠️ Note: If AccuBattery shows wear and tear of more than 50%, but the smartphone is working normally, it may be that the application is not properly calibrated.
Charge your phone to 100% | Disable battery optimization for the application |Do not use other monitoring utilities | Wait for 2-3 full discharge cycles-->
4.Discharge test: how to determine wear without programs
If you don't want to install third-party applications, you can do a manual discharge test, which is less accurate, but gives you a general idea of the battery status.
Instructions:
- Charge the Mi 9T to 100% and disconnect from the network.
- Turn on Airplane Mode and set the screen brightness to 50%.
- Run the video in Full HD on YouTube (cached) or play a local file.
- Take a look at the time it takes the charge to drop to 10%.
Results:
- ✅ 6-7 hours – battery in excellent condition.
- ⚠️ 4-5 hours – average wear (20–30%).
- ❌ Less than 3 hours – critical wear and tear, replacement is required.
This test doesn't take into account background processes, so repeat it 2-3 times for accuracy. If the results are very different, the problem may be the system's energy consumption, not the battery.
💡
For a more accurate test, use the PCMark Battery Test application, which simulates real load (web surfing, photo editing) and gives an objective estimate of the time of operation.
5. Physical Diagnostics: When the Problem Is Not in the Battery
Sometimes the symptoms of a dying battery are caused by other malfunctions.
- 🔌 Charging port – oxidation or contamination of contacts can cause slow charging and false discharge signals.
- 🔥 CPU overheating – if the smartphone heats up on simple tasks, the problem could be in the heat paste or chipset.
- 📱 Firmware - on some versions MIUI have charge display bugs (for example, jumps from 30% to 1%).
How to check:
- Connect the Mi 9T to another charger, and if the charge is stable, the problem is with the RAM.
- Try charging your phone in Safe Mode (hold the shutdown button → Safe Mode). If the battery is behaving normally, it's third-party software that's to blame.
- Light a flashlight into the charging port - if foreign objects or corrosion are visible, cleaning is required.
⚠️ Attention: If the Mi battery 9T bloated (visible on a raised screen or body warp), immediately turn off the phone and do not use it until the battery is replaced.
6.When to change the battery: wear rates for the Mi 9T
The manufacturer claims that the Mi 9T battery is designed for 500 full charge cycles (0 to 100%) with 80% capacity, in practice it is 2-3 years of active use, here are the reference points for replacing:
| Battery wear and tear | Symptoms | Recommendations |
|---|---|---|
| 0–20% | Minor reduction of working hours | We can continue to exploit it. |
| 20–40% | Fast discharge under load, heating | Monitor the temperature, reduce charging cycles |
| 40–60% | Sudden shutdowns, the charge lasts 2-3 hours | Prepare for replacement |
| 60%+ | The phone does not turn on without charging, bloating | Urgent replacement! |
If you decide to replace the battery, choose original spare parts (article MBJ406350 for Mi 9T). The cost of a new battery is about 1500-2500 rubles, the replacement work is 1000-1500 rubles.
💡
Even if the battery wears 30-40%, but the phone is satisfied with the time of operation, it is not necessary to rush to replace. Modern charge controllers (as in the Mi 9T) adapt to the degraded battery and prolong its life.