Xiaomi BN42: What is the battery model and how to replace it

Many Xiaomi and Redmi smartphone users are faced with the mysterious BN42 marking on their device’s body or when searching for a spare battery. Often the question arises: BN42 Xiaomi — what kind of phone model is hidden behind this code? In fact, the BN42 is not the name of the smartphone, but the factory index of the lithium-polymer battery, which was installed in popular devices of 2018-2019 release.

Understanding that the BN42 is a battery, not a phone model, is critical when buying repair parts. If you're looking for a new phone with this code, you won't find it in the catalogs, because it's an internal component. However, if your smartphone starts to run out quickly or turn off by 20%, this code will help you find a compatible replacement. In this article, we'll go into detail the specifications of the battery, how to distinguish the original from the fake, and give you a full manual on self-replacement.

Importantly, despite the age of the devices for which this battery is intended, the demand for quality BN42 batteries remains high.The market is oversaturated with low-quality copies that may not only solve the problem of autonomy, but also damage the smartphone power controller. Therefore, the original battery capacity of the BN42 is strictly 4000 mAh (typical) or 3900 mAh (minimal), and any significant deviations in the smaller direction speak of counterfeit.

Specifications and compatibility of BN42

The BN42 battery is a non-removable Li-Pol battery designed specifically for Qualcomm’s energy-efficient Snapdragon processors, which were used in mid-range devices, with a nominal voltage of 3.85 V, the standard for modern lithium polymer batteries, balancing energy density and safety, and is designed as a flat rectangle with a connector located in a specific zone, making it incompatible with other models without physical modification of the body.

The main compatibility of this model extends to two key devices that became hits in their time. First, it is the Redmi Note 5 Pro (known in China as the Redmi Note 5), which was widely adopted due to its good camera and performance. Second, the BN42 battery is used in the Xiaomi Mi 8 Lite, which featured a stylish design and glass back cover. Despite the differences in the appearance of smartphones, Xiaomi engineers used a single power platform to simplify logistics and production.

⚠️ Warning: Do not try to install the battery BN42 In the Redmi Note 6 Pro or Mi 8 (not Lite) model, although the names are similar, the geometry of the body and the location of the plume may differ, which will result in the inability to close the back cover or damage to the plume during assembly.

Below is a table with detailed technical parameters to help you identify the battery:

How to distinguish the original BN42 battery from a fake

The Xiaomi component market is unfortunately overflowing with replicas of poor quality. A fake BN42 battery can have a real capacity of 2,000-2500 mAh instead of the declared 4,000, which will lead to quick discharge. In addition, cheap copies often lack proper protection against overheating and overcharging, which creates the risk of bloating and even fire of the device. Therefore, the ability to visually and programmatically check the battery before buying or installing is a skill of the first necessity.

The first thing to look at is the quality of the printing and labeling. BN42 All the inscriptions are clearly marked, laser engraving or high-quality typographical paint that is not erased by a finger, QR-It is important to check for a holographic sticker with a protective code that can be verified on the official website of the manufacturer, although this is less common in the budget segment.

The second method of testing is software. After installing the battery (or connecting a new one before final assembly), it is recommended to use diagnostic tools. In the Xiaomi engineering menu or through applications like AccuBattery or AIDA64, you can actually have the capacity and condition of the cell. If the application shows wear and tear of 0% on the used battery or the capacity is much lower than the passport, this is clearly not the original.

• 🔍 Visual inspection of the plume: The original has a golden contact pad, smooth, without scratches or oxides. The plume is flexible, does not break when flexed lightly.
• 📏 Dimensions and weights: Original BN42 near-weight 80-85 If the battery is suspiciously light, then less active substance is used inside.
• 📱 Checking in MIUI: In some versions of the firmware when connecting a non-original battery, the system can issue a warning "Can not check the battery" in the settings.

Preparing for replacement: security tools and measures

Replacing the BN42 battery in the Redmi Note 5 Pro or Mi 8 Lite requires care and a minimal set of tools.The process is not technically complex, but requires attention to detail, since the back cover of the smartphone is glued and the internal components are tightly arranged. Before work begins, you need to ensure a clean, well-lit workplace so as not to lose small screws and damage the plumes.

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

1.A dryer or heating platform for softening the glue.

2. Plastic mediators (scapula) and suction cup.

3. a set of screwdrivers (Phillips cross #00 or #000).

4. Tweezers for the extraction of small details.

5.Isopropyl alcohol and new adhesive base (B-7000 or finished template) for fixing the back cover.

It is important to be safe when working with lithium polymer batteries. Damage to the battery housing with a sharp object can cause the electrolyte to instantly ignite. If you notice that the old battery is swelling, do not press it hard and do not try to pierce it. Work in a ventilated room and use safety glasses if possible.

⚠️ Attention: It is strictly forbidden to use metal tools to pick the battery from the case. Metal can break through the insulation and cause a short circuit, which will lead to a thermal reaction and fire. Use only plastic blades.

Step-by-step instructions for replacing the BN42 battery

The replacement process begins with the removal of the back cover. Since the Redmi Note 5 Pro and Mi 8 Lite have glass and glue, heat the device perimeter with a hairdryer to about 60-70 degrees (the glass should be hot to the touch, but bearable). After heating, glue the suction cup at the bottom of the back cover, pull it upwards, creating a gap, and gently insert a plastic mediator. Swipe the mediator around the perimeter, cutting the adhesive layer.

When you take the lid off, you'll see a plastic panel covering the main board and the battery, and it's secured with multiple screws.

1. Unscrew all visible screws on the plastic lining.
2. Remove the lining, opening access to the battery and plumes.
3. Find the battery connector to the motherboard, which is usually located on the top, under a metal screen or plastic protection.
4. Carefully unplug the plume using a plastic spatula.

The BN42 battery itself is glued to the frame of the case on a double-sided tape. To extract it, you can use a suction cup by pulling a special tongue tape (if it is preserved), or gently tamper with the battery with a plastic card on the opposite side of the connector. After removing the old battery, clean the landing place of glue residues, install a new BN42, connect the plume to a characteristic click and check the device's on before final assembly.

Typical problems after replacement and their solution

Even with the new BN42 battery installed correctly, users may encounter a number of software and hardware nuances. Android and the MIUI shell may not immediately correctly calibrate the new power source, manifested in percentage spikes (e.g., a sharp change from 40% to 15%) or incorrect display of operating time. Most of the time, this is solved by a calibration cycle: completely discharge the phone before turning off, then charge it to 100% in the off state without interrupting the process.

Another common problem is the system's "Abnormal battery temperature" or failure to charge, which may indicate that the temperature sensor located on the battery plume or on the board is not reading correctly. Check if the plume is compressed during assembly. It is also possible that the contacts in the charging connector, which coincidentally manifested during repairs.

• 🔋 Quick discharge: If new BN42 If you sit down in a couple of hours, check the usage statistics in your settings, maybe it's not the hardware that's to blame, but the background app that eats up the energy.
• 🌡️ Heating: Light heating in the area of the camera when charging is normal for fast charging. If the lower part is warming (where the battery is) and the phone turns off, this is a sign of a defective cell.
• ⚡ No fast charging: Make sure you use the original cable and power supply.Cheap cables may not support the Quick Charge protocol that the Redmi Note 5 Pro needs.

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To extend the life of the new BN42 battery, try not to keep the phone 100% charge and not to discharge to zero.

Recycling of old battery and ecology

Once you have completed the replacement, you are left with an old battery that can't just be thrown into the trash, lithium polymer batteries contain chemicals that are dangerous to the environment, and when they get to a landfill, they can oxidize, releasing toxins into the soil and groundwater, and even damaged batteries can catch fire in the garbage truck, putting the workers at risk.

There are several ways to properly dispose of a BN42 spent battery. Many cities have battery and battery reception points, often located in large supermarkets, electronics stores or specialty recycling centers, and many Xiaomi repair service centers accept old parts for recycling, provided you hand them a new order.

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Proper disposal of old batteries is not only a law, but also a contribution to the preservation of the environment, as lithium and cobalt are recyclable.