Xiaomi Redmi Note 9’s Complete Charging Guide: How to Save Battery for 3+ year-end

The Xiaomi Redmi Note 9, with its capacious 5,020 mAh battery, has become one of the longest-playing smartphones in its segment, but even this battery loses up to 20% of its capacity in the first year if it is not used correctly. In this article - only verified data from the technical documentation Qualcomm (manufacturer of the Snapdragon chipset) 720G Redmi Note 9) and Xiaomi engineers’ recommendations adapted for real-world use.

We will not only break down the basic rules (which everyone ignores), but also the hidden settings. MIUI, There are many things that affect charging, and myths that shorten battery life by 40 percent faster, like, did you know that using the original Redmi Note 9 charger is 12 percent more efficient than third-party adapters, even with the same specifications? This is due to Quick Charge 3.0 protocol and power controller calibration.

This article will be useful for those who have already noticed that the smartphone discharges faster, and those who just bought the Redmi Note 9 (or its modifications: Note). 9S, Note 9 Pro) and wants to maximize battery life.All tips tested on firmware MIUI 12–14 and relevant for devices produced from 2020 to 2023.

1. Technical specifications of the Redmi Note 9 battery: what you need to know before charging

The battery in the Redmi Note 9 is a 5020 mAh Lithium Polymer Battery (Li-Po) with a rated voltage of 3.85V. It consists of two cells connected in parallel, allowing for faster distribution of current when charging.

• 🔋 Charge type: Quick Charge 3.0 (maximum 18W), compatible with Quick Charge 4+ and USB Power Delivery (but without Wireless Charging).
• ⚡ Optimal charging current: 2.0–2.4A at 9V (peak mode).
• 📉 Number of cycles: 500 full cycles (discharge from 100% to 0%) to 20% capacity loss, and if properly operated, this can be increased to 800+ cycle.
• 🌡️ Operating temperature: from 0°C to 45°C, but the optimal range for charging is 10°C–35°C.

The power controller in the Redmi Note 9 automatically adjusts the current to the battery temperature and charge level, for example, when you reach 80%, the charging speed decreases by 30%, and after 90%, by another 50%, this is done to protect the cells from overheating and degradation. However, this logic can be changed through hidden settings. MIUI (about this in the section on optimization).

⚠️ Note: If your Redmi Note 9 suddenly starts charging slower than usual (e.g., from 0% to 100% over 3)+ Check the battery status through the engineering menu: enter the phone code ##4636##, then select Battery Information. Health should show good. If there is unknown or dead, the battery needs to be replaced.

2. Myths about charging Xiaomi Redmi Note 9: what actually harms the battery

There are a lot of smartphone charging tips on the Internet that not only fail to help, but also accelerate battery degradation.

• 🔌 "You have to completely discharge the battery once a month to calibrate, which was the case for nickel batteries 20 years ago. For Li-Po, deep discharge (0%) reduces the life of 1-2 cycles.
• ⚡ "Fast charging spoils the battery — no, if you use the original adapter. In the Redmi Note 9, the controller limits current when heated above 40.°C.
• 📵 "You can’t use your phone while charging, but intense tasks (games, video editing) increase the battery temperature by 5-10.°C, which speeds up wear.
• 🔋 "Charging at night kills the battery – only if the smartphone lies on a soft surface (overheating) or using a non-original cable.

One of the most dangerous myths is that the longer you charge, the better. In practice, keeping the Redmi Note 9 on charge for days means:

1. Constantly maintaining 100% voltage, which accelerates the oxidation of the electrodes.
2. Overheating due to background processes (e.g., updating applications over Wi-Fi).
3. Risk of overcharging when using low-quality adapters (even if they are “suitable” in power).

Xiaomi engineers recommend disconnecting your smartphone from the network when you reach 80-90%, unless you plan to use it immediately. MIUI Optimized charging (more about it in the next section).

3. Optimal settings MIUI battery life extension

MIUI It has a few hidden and explicit features that help control charging, and most users don't even know they exist:

Activation of "Optimized Charging"

This feature limits the charge to 80% and then dosed to 100% of the time you normally turn off your smartphone (based on your habits).

1. Go to Settings. → Battery and productivity → Optimized charging.
2. Turn on the slider and set up a schedule (for example, if you charge your phone at night, specify wake-up time).

Turning off background processes during charging

Apps like Facebook, Instagram or TikTok can drain the battery even while charging, creating a paradoxical situation: the smartphone warms up, and the percentage of charge increases slowly.

1. Open Settings → Applications → Permissions → Autostart.
2. Turn off auto-start for unnecessary applications.
3. B Settings → Battery → Select Battery Mode Select Charge Savings for Charging Time.

Temperature settings

Redmi Note 9 automatically reduces charging current when heated above 40°C, but this threshold can be changed through the engineering menu (at your own risk:

1. Enter the code ##284## (battery test) in the Phone app.
2. Check the current temperature if it's above 35.°C, disconnect the smartphone from the network and let it cool down.

Check the battery temperature (should be below 35)°C)|Use the original cable and adapter|Turn off background apps|Remove the cover (if it is thick)|Do not place your phone on soft surfaces (sofa, bed)-->

Shutting down fast charging (if necessary)

If you prefer gently charging, you can turn off Quick Charge 3.0:

1. Go to Settings. → Additionally. → Special facilities → Developer options.
2. Activate Developer Options (click 7 times on Version) MIUI phone).
3. Return to Special Opportunities → Developer Options and Turn Off Fast Charging.

After that, the smartphone will be charged with standard current 5V/2A (power) 10W), which will extend the battery life, but will increase the charging time with 0% before 100% s 2 hourly 3.5 hours.

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If you frequently charge the Redmi Note 9 from powerbank, use models that support Quick Charge 3.0 (such as Xiaomi Mi Power Bank 3 Pro).

Step-by-step: how to charge the Redmi Note 9

Now, let's get to the point. Here's the optimal charging algorithm that minimizes battery wear:

Preparation for charging

• 🔌 Use the original cable and adapter from the kit (or certified analogues labeled Quick Charge 3.0).
• 🌡️ Check the temperature of your smartphone: if it is hot (above 35)°C), let cool for 10-15 minutes.
• 📴 Close all resource-intensive applications (games, navigators, video players).

Charging process

1. Connect your smartphone to the charger. The lock screen will display an indicator that says Quick Charge (if you use Quick Charge).
2. If charging is slow (e.g. 5W instead of 18W), check:

80%

Optimized charging

After charging

• ⚡ Do not leave the smartphone on the charge "on reserve" - after 100%, the controller turns off the power, but when it falls to 99%, it recharges again, creating microcycles.
• 🔋 If you don’t plan to use your phone for a long time (for example, overnight), it’s best to leave it with a charge of 40-60% – this is the optimal level for storing it.

The average charging time of the Redmi Note 9 is between 0% and 100% when using the original 18W adapter:

• 0%–50%: ~30 minutes.
• 50%–80%: ~40 minutes.
• 80%–100%: ~50 minutes (due to reduced current).

⚠️ Warning: Never use the Redmi Note 9 while charging if it is lying on a charging station or powerbank in an enclosed space (such as a bag) and this can cause the battery to overheat and bloat. In 2021, Xiaomi recalled a batch of the Redmi Note 9 Pro because of such cases.

5. How to check the condition of the battery and its wear

Over time, the battery capacity decreases, and there are several ways to find out the current battery status in the Redmi Note 9:

5.1. Through the engineering menu

Enter the phone code in the appendix:

##4636##

Select Battery Information. Pay attention to the parameters:

• The charge level is the current percentage.
• Health (health) should be good.
• Temperature - optimally 25-35°C.
• Stress - at 100% should be ~4.35B.

5.2. Through the AccuBattery application

This third-party app (available on Google Play) shows:

• 📊 Real battery capacity (e.g. 4500 mAh instead of 5020 mAh at 10 wear%).
• 🔋 Discharge speed in standby and under load.
• 📈 Graphic degradation of the container during use.

Example: If the AccuBattery has a capacity of 4,000 mAh, it means that the battery is worn out by 20% and needs to be replaced.

Indirect indications

The fact that the battery has degraded, say the following symptoms:

• ⚡ Smartphone discharges by 10-15% per night in standby mode (with Wi-Fi and mobile data turned off).
• 🔥 The body is very hot even with light load (for example, browsing social networks).
• 📉 The percentage of charge "jumps" (for example, from 30% immediately to 10%).
• ⏳ Charging time to 100% increased by more than 30% compared to the new state.

If the capacity has fallen below 3500 mAh (which corresponds to wear and tear). ~The average cost of the original battery for the Redmi Note 9 is 1500-2000 rubles (2026), you can do the replacement yourself (there are video instructions) or in the service center.

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If the battery capacity has fallen below 60% of the original, it will cost less to replace than a smartphone repair due to a sudden shutdown or bloating of the battery.

6. Frequent User Errors and How to Avoid Them

Even experienced Xiaomi owners sometimes make mistakes that shorten battery life.

Use of substandard accessories

Cheap cables and adapters can:

• 🔌 Do not support the Quick Charge 3.0 protocol, which makes the smartphone charge longer and warms up more strongly.
• ⚡ Give unstable voltage, which leads to microdischarges and wear of the power controller.
• 🔥 Induce a short circuit (in rare cases).

Signs of a poor adapter:

• The swelling is a bit of a stretch (the percentage is rising and falling).
• Adapter is very hot (above 50)°C).
• The smartphone defines charging power as 5W instead of 18W.

Charging at extreme temperatures

Charge Redmi Note 9 at a temperature below 0°C or higher than 45°C is absolutely not allowed. This is what happens in these cases:

• 🥶 In cold (-10)°C) the battery capacity temporarily drops by 30-50% and may not recover when returned to heat.
• 🔥 In the heat (>45°C) the electrolyte inside the battery begins to decompose, resulting in irreversible loss of capacity.

Continuous maintenance of 100% charge

Many people leave their smartphone on charge all night long or connected to a powerbank during the day, leading to:

• 📉 Accelerated degradation of the anode (capacity loss by 2–3% per month).
• 🔋 Overheating due to background processes (updates, synchronization).
• ⚡ Microcycles charging (when the controller turns off, it turns on power to maintain 100 times%).

Solution: Use Optimized Charging in MIUI or turn off power when you reach 80-90%.

6.4 Ignoring firmware updates

Xiaomi regularly releases updates that optimize power management. MIUI 13 added:

• 🔄 Smart current distribution during fast charging.
• 📉 Optimizing the background activity of applications.
• 🌡️ Improved Battery Temperature Control.

To check for updates, go to Settings → The phone. → Updating the system.

7. Alternative charging methods: what can and cannot

In addition to standard charging from the outlet, the Redmi Note 9 supports several alternative methods, let’s analyze their pros and cons:

Charging from a computer or laptop

You can charge the Redmi Note 9 via USB-computer port, but there are nuances:

• ✅ Pluses:
• ❌ Cons:

Charging from powerbank

Using an external battery is convenient for travel, but:

• ⚡ Choose Powerbank with Quick Charge 3.0 support (e.g. Xiaomi Mi Power Bank 3 Pro).
• 🔋 Avoid cheap models without overload protection – they can damage the smartphone’s power controller.
• 🌡️ Watch the temperature: if powerbank is warming, turn it off.

Wireless charging (via adapter)

Redmi Note 9 does not support wireless charging out of the box, but you can use an adapter with a wireless charging system. USB-C - The Qi receiver:

• ⚠️ Risks:

Recommendation: It is best not to use this method unless there is an urgent need.

Charging from a car lighter

If you frequently charge your smartphone in your car:

• 🚗 Use an adapter with Quick Charge 3.0 (e.g. Xiaomi Car Charger).
• 🌡️ Avoid charging when the engine is running in the heat - the temperature in the cabin can exceed 50°C.
• 📵 Do not leave your phone in the sun (for example, on a torpedo).

Important: If you use the Redmi Note 9 as a navigator, plug it into charging before the trip starts to avoid dripping on the way.

8 What to do if the battery is already worn out: restoration and replacement

If the battery capacity has dropped below 70 percent of the original capacity, it's time to change it.

Replacement of the battery by itself

For the Redmi Note 9, it's a simple procedure, but it requires care.

• 🔧 Sets of screwdrivers (Phillips #00 and spudger for disconnecting plumes).
• 🔋 New battery (original Xiaomi) BM4B, articular MDY-11-EM).
• 🧲 Removal suction cup.
• 🔥 Hair dryer or heater plate for softening glue.

Step-by-step:

1. Turn off your smartphone and remove it. SIM-map.
2. Heat the back cover with a hair dryer (temperature 60–70)°C) and gently apply her spudger.
3. Unscrew 12 screws holding the metal plate.
4. Disconnect the battery plume (it is under a black insulation tape).
5. Carefully remove the old battery (it is glued, so put it with a plastic spatula).
6. Install a new battery, plug in the plume and assemble the phone in reverse order.

If you confuse polarity or damage the contacts of the plume, the smartphone can:

- Not included at all (motherboard diagnosis is required).

- Incorrect charge level (e.g. 0%)