How to replace the battery on Xiaomi Mi 8: the complete guide

Smartphone Xiaomi Mi 8, released in 2018, still remains a popular device due to its powerful processor and high-quality AMOLED-But the lithium-ion batteries are not spared, and after a few years of active use, owners begin to notice a sharp drop in autonomy, the device can discharge in front of their eyes, turn off at 20% charge or swell, deforming the back cover. In such situations, replacing the power source becomes the only reasonable solution to extend the life of the gadget.

Self-replacement of the battery is a complex but doable process that requires precision, special tools and understanding of the device of modern smartphones. The body of the Mi 8 does not have screws on the outside, which involves using suction cups and heating elements to safely open. Wrong actions can lead to damage to the plumes, rupture of the display plume or even bloating a new battery if installed improperly. This article will help you go this way with minimal risks.

Before you start disassembling, you need to objectively assess your skills and equipment. If you have never held thin plastic mediators in your hands or do not know how to turn off the battery plume without short circuit, you should contact the service center. However, if you are confident in your abilities and are willing to act slowly and thoughtfully, this guide will be your reliable assistant in the recovery of the Mi 8.

Diagnostics and workplace preparation

The first step is to determine exactly what the current battery is, and users often confuse software failures with the physical degradation of the battery chemistry, and first, you need to do a visual inspection: if the back glass panel has risen or moved away from the frame, this is a sure sign that the battery is swelling, in which case you can absolutely not use the device, because the pressure on the display can cause it to rupture.

If there are no external signs, you should use software diagnostic methods. MIUI There's a hidden engineering menu that allows you to check the status of the battery ##6485##. In the list of parameters you are interested in values MB_06 (battery status; and MB_00 (The percentage level of charge is also worth paying attention to the parameter. MF_02, which shows the number of full charging cycles; if the number exceeds 500-600, element resource is exhausted.

Preparing the workplace is a critical step that is often ignored by beginners. You will need a clean, well-lit surface, preferably with antistatic coating or just a clean desk without pile. All the small parts are better folded in a magnetic mat or special containers with cells, so as not to lose screws of different calibers. The lack of dust and moisture in the room also plays a role, since the inside of the smartphone should not be contaminated during the repair process.

To successfully replace, you will need the following set of tools:

• 🔧 Set of screwdrivers (cross Precision and flat).
• 🔥 Hair dryer or heating platform (to soften glue).
• 📱 Suction and thin plastic mediators (scapula).
• 🧴 Isopropyl alcohol or special solvent B-7000.
• 🔋 New battery model BM3H (original).

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Use only high-purity isopropyl alcohol. Water or alcohol with impurities can cause corrosion of contacts or short circuit when power is supplied.

Safe disassembly process

You should start working only after completely switching off the device. Xiaomi Mi 8 has a glass back cover that is attached to a double-sided tape around the perimeter and in the center. To ease the adhesion of the adhesion of the adhesive, you need to heat the perimeter of the body. The optimal temperature is 80-90 degrees Celsius; you should warm up for 2-3 minutes, constantly moving the hair dryer, so as not to overheat the display matrix on the front side.

After heating, install a suction cup at the bottom of the back cover, receding about 1-2 cm from the edge. Pull the suction cup up, creating a small gap between the glass and the frame. Insert a thin plastic mediator into the resulting gap carefully. It is important not to plunge the blade deeper than 3-4 mm, so as not to damage the plumes running along the side faces, especially in the area of the volume and inclusion buttons.

Move the mediator along the perimeter, cutting the adhesive layer. Pay special attention to the corners where the adhesive holds the strongest. If the lid stops moving, the heating procedure should be repeated. Don't use excessive force: the glass is fragile and can burst, and the fragments can damage the internal components. Once the lid is separated, remove it and put it in a safe place.

So right after you take the lid off, you'll see a plastic safety panel covering the main components, and it's locked with several screws, unscrew them and carefully remove the plastic, and underneath it you'll have access to the motherboard, the main camera module, and of course the battery, and you'll have to turn off the power before you touch the other connectors.

Dismantling of the old battery

Inside the Xiaomi Mi 8, the battery takes up most of the space and is glued to the middle frame on a powerful two-way tape. Before you try to remove the battery, you need to disconnect its plume from the motherboard, you need to do this with a special plastic blade or nail, gently putting the connector up. Metal tools are forbidden to use to avoid short circuit contacts.

Removing the battery is the riskiest step, and underneath the battery are the plumes of the display and touchscreen that run underneath, and if you pull the battery sharply or prick it with a tool, you can damage the plumes or cause the damaged battery to catch fire. It is recommended to use special pull-up tapes (pull-tabs) if they are preserved, or carefully poke the edges of the battery with a plastic card, before dripping a little alcohol under the edge.

Never use metal objects such as needles or blades to swell the battery. A lithium-ion battery puncture results in instant thermal runaway, accompanied by a caustic smoke and fire. If the battery is too swelled, handle it with extreme caution, do not squeeze it or pierce it.

⚠️ Warning: If during the extraction process you damaged the battery shell and felt a sharp chemical smell, immediately stop work, ventilate the room and dispose of the battery in a special container.

Once the old battery is removed, you need to carefully clean the seat of the residue of the old glue. Use a plastic card and isopropyl alcohol. The surface must be perfectly flat and clean so that the new battery will lie tight and evenly. Any irregularities can lead to spot pressure on the new battery.

Installation of a new battery and assembly

The new BM3H battery needs to be ready for installation. Often new batteries come with factory protective films on the contacts, they need to be removed. Also, the original protection module (BMS) must be re-adhesed to the new battery or use a special double-sided tape if the design requires it. In the case of the Mi 8, it is usually enough to apply new adhesive strips to the battery body or to the frame of the smartphone.

Put the new battery in the compartment, making sure it lies flat and doesn't protrude over the edges of the frame. Connect the plume to the motherboard before the characteristic click. Don't turn the phone on right away! First, check the voltage on the battery contacts with a multimeter, if possible, or just visually make sure there are no distortions.

Now you can preassemble, put the plastic shield in place, and twist all the screws. It's important not to pull the screws, because this can lead to cracks in the plastic or damage to the thread. Then plug in the display plume (if it's been disconnected) and try to turn the device on by pressing the power button.

If the smartphone is on and showing charging, you can start the final assembly. Apply a new glue (B-7000 or analog) on the frame of the case in a thin layer. Apply the rear glass cover and press it tightly around the perimeter. For fixation, it is recommended to use stationery gums, wrapping them around the perimeter of the phone, and leave the structure to dry for 1-2 hours.

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High-quality sealing and uniform pressing of the lid is the guarantee that the smartphone will retain dust protection and the new battery will not shift when falling.

Calibration and primary start

After the battery is replaced, the Android system may not display the charge level correctly, since the power controller is “accustomed” to the parameters of the old worn-out element. For the Xiaomi Mi 8 to correctly determine the percentages and operating time, you need to conduct a calibration procedure. This is especially important if you notice a jump in charge (for example, from 30% a sharp transition to 5%).

Calibration is simple, but it takes time. Completely discharge the new battery before the smartphone is turned off. Then put the phone on charge when it's off and wait 100 percent. Once you reach full charge, don't disconnect the device for another 1-2 hours. This will allow the controller to write down the actual capacity limits.

Then turn on the phone without disconnecting the charger, and make sure the charge level is still 100%. If the rate is down, get back to 100% and wait again. Repeat the cycle of full discharge and charge 1-2 times. Usually after 2-3 cycles, the power controller (Fuel Gauge) adapts to the new chemistry of the element.

The table below shows the main parameters that are worth checking after replacement:

Possible problems and solutions

Even with a careful assembly, there can be unexpected situations. One of the common problems is that the smartphone does not turn on after replacement. First of all, check if the battery connector is tightly latched. Sometimes you need to press it with a little effort through the protective plate. It is also worth checking the integrity of the plume itself: if you sloppyly remove it is easy to tear.

Another common problem is the lack of charging or the message "Accessories not supported" which may indicate that the new battery has an unoriginal controller that the MIUI system cannot read correctly, in some cases, helps resetting to factory settings, but most often this is a feature of cheap counterparts.

If the phone is warming up in the camera or processor area when it is down, you may have screwed the protective plate poorly or damaged the heat pad.The heat sink in the Mi 8 is implemented through graphite layers and a metal frame; a contact disruption can lead to local overheating.

⚠️ Note: If you experience a rapid charge loss after replacement (more than 5% per hour in standby mode), it is possible that the battery is defective or has too low real capacity.

Remember that after opening the case, the smartphone loses moisture protection if it was declared by the manufacturer. Be careful with further moisture and dust. Check the condition of the cover regularly and update the adhesive layer if necessary.

Frequently Asked Questions (FAQ)