Replacement of the battery on Xiaomi Mi 9T: detailed instructions with photos and tips

Why Xiaomi Mi 9T Battery Fails and When to Change It

Xiaomi Mi 9T (also known as Redmi K20 in some regions) was released in 2019 with a lithium polymer battery with a capacity of 4000 mAh. Even with careful use after 2-3 years, the original battery begins to lose up to 30-40% of capacity, which manifests itself in rapid discharge, sudden outages with 20-30% charge or bloating. The manufacturer claims a resource of 500-800 charging cycles, but in practice this figure is often reduced due to overheating, the use of non-original chargers or deep discharges.

The main signs that the battery is time to change:

• 🔋 The phone discharges in 3-4 hours with moderate use (social networks, instant messengers).
• 🔌 Charging jumps (for example, from 50% immediately to 20% or the phone turns off with 15% of the remainder).
• 📱 The case is swollen - a noticeable gap between the screen and the back cover or the smartphone "walks" on a flat surface.
• ⚡ The phone warms up more than usual during charging or work.

If you see at least two of these symptoms, battery replacement is inevitable. You don't have to delay the procedure: a bloated battery can damage the display or motherboard, which will lead to expensive repairs. In addition, the Mi 9T has a glued body, and the longer the worn-out battery is in use, the harder it is to remove it without the risk of tearing the plumes.

What battery to choose for Xiaomi Mi 9T: original vs analogues

The original battery for the Mi 9T has the article MB-J12B (or BM4D in some versions) and a capacity of 4000 mAh at a voltage of 3.85V. However, after 2021, Xiaomi stopped supplying original batteries to retail, so the market is dominated by analogues from third-party manufacturers. It is important to understand that even the “original” batteries in the Xiaomi package, bought on AliExpress or Amazon, with a 90% probability are fakes.

When choosing a battery, pay attention to:

• 🔍 Capacity: Must be at least 3,900–4,000 mAh Batteries with a capacity of 4,200–4,500 mAh are often poor quality and quickly degrade.
• 🏭 Manufacturer: reliable analogues are produced by Patona, Baseus, Remax (Pro series — ZMI (subbrand).
• 📦 Set: the set should be adhesive strips for fixation and insulation film (to avoid short circuits).
• 💰 Price: high-quality battery costs 1500-2500 rubles. Cheap options (up to 1000) ₽) Often have an understated real capacity.

Critical: the battery should have protection against overcharging and short circuit (marked "PTC" or "Protection Circuit"). Buy only from trusted sellers with a guarantee of at least 6 months. Avoid batteries without labels or with labels like "Super Capacity" - this is a sure sign of counterfeiting.

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Check reviews for a specific battery model before buying. Users often complain of rapid wear and tear or capacity mismatch. For example, AliExpress can filter reviews for keywords like “discharge” or “bloating.”

Preparing for replacement: security tools and measures

Replacing the battery with the Xiaomi Mi 9T requires care and special tools, and unlike smartphones with removable covers (such as the Redmi 4A), the body is glued together and the battery is glued to the back.

• 🔧 Plastic blades (2-3 pieces) for dissociating the body.
• 🔨 Thin screwdriver (cross, size) PH00 or PH0).
• 🔥 Hair dryer or thermal air station for softening glue (temperature 60-80)°C).
• 🧲 Suction cup (diameter 4-5 cm) for lifting the screen.
• 🛠️ Tweezers with thin ends for working with plumes.
• 🧴 Isopropyl alcohol (90%+) glue-residue.

Security measures:

⚠️ Attention: Lithium polymer batteries can ignite if punctured or flexed, and if the battery is swelling, don't try to pierce it, it will cause a chemical reaction and a possible fire, and then you should contact the service center.

Also consider:

• 📵 Turn off the phone and remove it. SIM-pre-disassembly.
• 🔌 Do not use metal tools to tamper with the battery - only plastic blades.
• 🕒 Stock up on time: the first time the procedure can take 1.5-2 hours.

If you don’t have experience in electronics repair, practice on an unnecessary smartphone or watch video disassembly on YouTube (Fixez or Repair Universe channels shoot detailed guides on Mi 9T).

Is the phone off the grid?|Is there a spare? SIM-card (in case of damage to the tray)|Is the workplace ready (clean surface, good lighting)|Is the device 20-30% charged (to avoid deep discharge during testing)|-->

Step-by-step instructions for replacing the battery

Now, to the process itself, follow the instructions strictly to avoid damage.

Step 1: Disassembly of the hull

1. Turn off the Mi 9T and place it up on a soft surface (such as a napkin).

2. heat the hair dryer back cover around the perimeter for 2-3 minutes, keeping it at a distance of 5-7 cm The glue will become softer, and the cover will be easier to separate.

3. With a suction cup, lift the screen from the bottom edge (where the charging connector is located), insert a plastic blade into the resulting gap and carefully guide it along the body, separating the clips.

⚠️ Warning: Don't pull the lid on the side of the volume or power buttons, because there are tails of the side keys that are easy to break!

Step 2: Turn off the plumes

1. Once you remove the lid, you'll see the battery covered with black film. Don't pull it, it's short circuit protection.

2 Unscrew 4 screws that fix the metal plate above the battery connector (they can be under the fillings - gently puncture them with a needle).

3. Put a plastic blade on the battery socket and disconnect it, and now the phone is completely off, and you can move on.

Step 3: Remove the old battery

1. Put a plastic blade on the battery from any angle. If it is glued heavily, heat it with a hair dryer (not higher than 60°C!).

2 Pull by special black tongues (if any) or poke the battery around the perimeter. Do not use metal tools!

3. After extraction, inspect the battery tray: remove the residue of glue with alcohol and check if there is damage to the plumes.

Step 4: Installation of a new battery

1. Remove the protective film from the new battery and glue it to the place of the old one, slightly pressing.

2. Connect the battery connector to the motherboard. Make sure it sits tight -- sometimes you need a light tap.

3. twist back the metal plate and check if there are any extra screws left.

Step 5: Assembly of the phone

1. Put the plumes in their places (they should lie freely, without tension).

2. Stick back cover. This can be done with double-sided tape or the original B-7000 glue (a thin layer applied around the perimeter).

3. Place the phone under the press (for example, put a heavy book on top) for 10-15 minutes to get the glue.

After assembly, do not turn on the phone immediately - let the glue dry for 30-60 minutes.

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The most common replacement mistake is a loose plume fit or a skewed battery, which leads to charging problems or sudden shutdowns. Always check the symmetry of the installation before the final assembly!

Calibration of the new battery and check of operation

Once the battery is replaced, it needs to be calibrated so that the charge controller can correctly determine the level of charge, and without calibration, the phone can show an incorrect percentage or quickly discharge.

How to do this:

1. Charge your phone to 100% original charger (18W power for Mi 9T).
2. Turn off charging and use the phone until it is completely discharged (until it turns off itself).
3. Connect the charge and charge again to 100% without interruptions.
4. Repeat the discharge-charging cycle 2-3 times.

Also check:

• 🔌 Charging speed: with the original Mi adapter 9T It should charge up to 50% in 30 minutes.
• 📊 Chart of discharge in Settings → Battery: It should be smooth, without sudden jumps.
• 🌡️ Battery temperature: when charging it should not exceed 40°C (checked in the engineering menu code ##4636##).

If the phone is not switched on after replacement:

• Check if the battery connector is tight.
• Make sure the display plume is not damaged (this is a common problem when disassembling).
• Connect the charge for 10-15 minutes – sometimes the controller needs time to initialize the new battery.

Frequent Mistakes and How to Avoid Them

Even with a careful replacement, users often face problems, and here are the most common mistakes and ways to prevent them:

Another common problem is that the new battery will blow up in a few months, and it's because of:

• 🔌 Use of non-original chargers (especially with power output above) 20W).
• 🌡️ Overheating (for example, if the phone is lying on a charger in direct sunlight).
• 📉 Deep digits (below 5%).

To extend the life of a new battery:

• 🔄 Avoid charging to 100% – optimal range of 20–80%.
• ❄️ Do not use your phone in the cold (below). -10°C) or in hot conditions (above) +35°C).
• 🔌 Turn off charging after reaching 100% (don’t leave overnight).

FAQ: Answers to Frequent Questions