How to check the battery on Xiaomi Redmi Note 9 Pro: from the code *#*#4636#*#** to disassembly

Xiaomi Redmi Note 9 Pro with its capacious battery 5020 mAh initially pleased with long work without recharging. But after 1.5-2 years, many owners notice that the smartphone discharges in half a day, turns off at 20-30% charge or overheats during charging. The reason is almost always the same – battery degradation. Fortunately, you can check its condition without visiting the service center, from hidden engineering menus to specialized applications.

In this article, we've got 5 working methods for diagnosing the Redmi Note 9 Pro battery, including those that don't require root rights. You'll learn how to determine real battery wear, detect bloating, check current consumption, even estimate the remaining resource in charging cycles. And what to do if the smartphone shows 100% charge, but turns off after an hour.

1. Check through the engineering menu (#4636##)

The fastest way to get data about the battery is to use a hidden engineering menu, which is available on all Xiaomi smartphones without additional applications. MIUI 14) this code can be blocked. If nothing happens after entering, proceed to the next method.

How to open the engineering menu:

• 📱 Open the Phone app** and enter the combination: ##4636##.
• 📊 Note the parameters: Level - current percentage in numbers (may differ from the indicator in the status bar). Voltage - norm for the Redmi Note 9 Pro at 100% charge: 4.35-4.40 V. If the value is below 3.7 V at 20% charge - the battery is severely degraded. Temperature (optimal 25–40)°C. Exceeding 45°C when charging or loading indicates a malfunction. Health - if Good is indicated, battery is normal. Unknown or no value is a sign of problems.

⚠️ Attention: On some firmware MIUI The health parameter may not be there. It doesn't mean the battery is faulty, it's just the manufacturer hid the data.

If the voltage at 100% charge is below 4.2 V and the smartphone is turned off by 30-40%, this is a clear sign of wear and tear of the battery, in which case its capacity has dropped by at least 30-40% from the original.

2.Visual inspection: signs of battery 'blown up'

Physical battery deformation is one of the most dangerous malfunctions. Xiaomi Redmi Note 9 Pro lithium polymer batteries can swell when overheated or deeply discharged, resulting in:

• 🔋 Disparity of the body seams (gap between the screen and the back cover).
• 📱 Convexities on the back panel (especially noticeable if you put the smartphone screen down on a flat surface).
• 🔌 Charging problems (the cable does not fit tightly into the connector due to deformation).
• 🚨 Unintentional shutdown when pressing the body (the battery contacts depart).

How to check:

1. Put your smartphone on the table with the screen down.
2. Lightly press the center of the back cover – if it “plays” or flexes, it is a sign of bloating.
3. Illuminate the flashlight along the body seams - if a gap of more than 0.5 mm is visible, the battery is deformed.
4. Try inserting a charging cable – if it comes in tightly or at an angle, it’s likely the battery is pressing on the connector.

⚠️ Warning: If you find bloating, immediately stop using your smartphone. The risk of a fire or explosion of the battery increases significantly during further operation.

On the Redmi Note 9 Pro, bloating is often seen in the camera area, due to the location of the battery under the top of the body. If the lenses become "recessed" or the back cover in this place is raised, this is an alarm.

3. Diagnostic applications: AccuBattery, CPU-Z and MIUI Battery Doctor

If the engineering menu doesn't give you the full picture, use specialized utilities that show real capacity, number of charging cycles and wear rate.

AccuBattery gives the most accurate data.

1. Charge your smartphone to 100% and calibrate the app (follow the hints).
2. Use your phone as normal until it is discharged to 15-20%.
3. In the Health section, look at Estimated capacity, compared to a factory capacity of 5020 mAh.

Example: If AccuBattery shows 3800 mAh, battery wear is: (5020 – 3800) / 5020 × 100% ≈ 24%.

This means that the capacity has decreased by a quarter, and the discharge rate will increase.

Charge your smartphone to 100% original RAM|Disable battery optimization for the application in settings MIUI|Do not use your phone during calibration|Repeat the test 2-3 times for accuracy-->

CPU-Z Run a performance test (Benchmark section) and monitor Battery Level** in real time. If the voltage drops below 3.5 V at 30% charge, the battery is critically worn out.

4. Test of working time: how to detect a fast discharge

If the battery is running out too quickly, but the applications show normal wear and tear, the problem may be software errors or background consumption.

1. Charge the Redmi Note 9 Pro to 100% and disconnect from the network.
2. Enable flight mode (to eliminate network influence).
3. Start the stop stopwatch and leave the smartphone alone (screen is off).
4. After 8 hours, check the remaining charge.

Normal results for the Redmi Note 9 Pro:

• 🔋 0–3% loss in 8 hours – battery in excellent condition.
• 🔋 4–7% loss – normal wear and tear (1–2 years of use).
• 🔋 8-15% loss – severe wear or background processes.
• 🔋 More than 15% - critical problems (subdued, short circuit).

If the discharge is going too fast, check:

• 📱 Background applications: go to Settings → Battery → Battery usage and see which programs consume the most.
• 🔄 Auto Updates: Turn off automatic app updates on Google Play.
• 📡 Network: weak signal 4G/5G It increases the flow rate. Try switching to 3G.

⚠️ Warning: If a smartphone runs 20 to 30 percent per night in flight mode, it almost always means a hardware malfunction of the battery.

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To speed up the test, discharge your smartphone to 50%, then turn on flight mode and launch the video on YouTube at maximum brightness. Normal discharge time to 10% is at least 3-4 hours.

5.Charging current check: why the smartphone is slowly charging

If the Redmi Note 9 Pro charges longer than 2.5 hours from the original 33W RAM, the problem may be:

• 🔌 Cable or adapter (damaged, unoriginal).
• 🔋 Battery (high internal resistance due to wear and tear).
• 📱 Connector USB-C (oxidation, pollution).
• 🔧 Firmware (mistakes in power management).

How to check the charging current:

1. Install the Amperé (or AccuBattery) app.
2. Connect the original 33W RAM and start charging.
3. Look at the current current (in mA) in the app.

Normal values for the Redmi Note 9 Pro:

• 🔌 3000-3500 mA in the first 30 minutes (fast charging).
• 🔋 2000–2500 mA charge from 30% to 80%.
• 🛑 Less than 1000mA – a problem with cable, RAM or battery.

If the current is below normal:

• Try another original cable (better from the set).
• Clear the connector. USB-C dust with a toothpick (carefully!).
• Check charging from another device (like the Redmi Note 10 Pro).
• If the current is still low - the battery is worn out and does not hold the charging current.

Important: On non-original memory, the smartphone can show charging, but in fact the current will be 500-800 mA. This leads to overheating and accelerated wear of the battery.

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If the charging current drops to 0 mA and the smartphone stops charging, it's a sign of a break in the power chain, and most often the charging controller is to blame, not the battery itself.

Disassembly and multimeter: for experienced users

If all software methods fail and the battery behaves strangely (for example, the smartphone turns off at 50% charge), you can check the voltage directly on the contacts of the battery.

• 🛠️ Set of screwdrivers (star) T3, flat).
• 📟 Multimeter (constant voltage measurement mode up to 20 V).
• 🧤 Plastic blade for opening the body.

Procedure:

1. Turn off your smartphone and remove the tray for SIM-map.
2. Heat the back cover with a hair dryer (temperature 60–70)°C) or use a suction cup to separate it from the body.
3. Unscrew 12 screws around the perimeter (don't lose!).
4. Carefully disconnect the battery plume (it is under a black insulation tape).
5. Connect the multimeter probes to the battery contacts (red — «+», black — «–»).

If the voltage is below critical, the battery is irreversibly damaged and must be replaced.

• 🔥 Bloating (if the battery is thicker than 5-7 mm in the center).
• 💧 Electrolyte dashing (white plaque on contacts).
• 🔌 Oxidation of contacts (green or black coating).

⚠️ Attention: If you've never disassembled a smartphone, you should have a specialist in charge of this procedure. The risk of damaging the plumes or shortening the battery is very high. The cost of replacing the battery in the service is 1500-2500. ₽, What is cheaper to repair after a failed disassembly.

After checking, assemble the smartphone in reverse order. Make sure all plumes are tightly connected and the screws are twisted with force (but not pulled!).

What to do if the battery is faulty?

If the diagnosis shows critical wear or bloating, you have three options:

Selection recommendations:

• 🔧 If the smartphone is warranty – only official service (otherwise the warranty will burn down).
• 💰 If your budget is limited, look for workshops with a minimum 6-month warranty.
• 🛠️ If you have experience disassembling – order a battery with a marking BM4X (Original for Redmi Note 9 Pro).

After the battery is replaced:

• Calibrate it: charge to 100%, discharge to 0%, then charge again to 100%.
• The first 3 cycles avoid intense loads (games, video shooting).
• Use only the original or certified 33W RAM.

Important: A new battery can run out faster than usual for the first 2-3 weeks, which is normal. Lithium polymer batteries need time to latch.

FAQ: Frequent questions about the Redmi Note battery 9 Pro