The Redmi 8 battery model name is BN51, sold as 5000 mAh typical and 4900 mAh rated. Most listings give BN51 for the Redmi 8A and 8A Dual too, so the three appear to share one cell. BN51 is a Xiaomi Li-ion polymer cell.
People search this phone as "redmi 8a battery model number" or even "mi 8a battery model name", but there is no phone called Mi 8A. The names to separate are Redmi 8, Redmi 8A, Redmi Note 8 and the older Mi 8. BN51 covers only the Redmi 8 and 8A models, and the label on your cell has the final word.
Quick facts
Step by step
Find out which Redmi 8 you hold
Open Settings, tap About phone and read the device name. If it is not clear, type model in the Settings search bar. The retail box also prints the name.
Keep the Note 8 and Mi 8 out of the search
Only Redmi 8 and Redmi 8A are in this group. A phone named Redmi Note 8 or Mi 8 has a different pack, so do not carry the code across.
Have the old battery read by a technician
The sealed back must be opened first. The code
BN51should then be visible on the cell sticker beside the capacity figures.Compare the new pack before it goes in
Put old and new side by side. Code, connector shape, thickness and weight should all agree. Leave the glued old pack to the technician.
Redmi 8A battery model: same pack or not
Many owners ask for the Redmi 8A battery model separately, because the 8A is the cheaper sibling. Listings still point to the same BN51 pack, and the 5000 mAh figure is quoted for both phones. Camera and some other parts differ between them, so screen-on time may not be identical, but the battery itself is described as one and the same.
The number in the name is where mistakes begin. The Redmi 9A is a newer phone with its own page, so open the Redmi 9A battery page before you pick a pack for it. Likewise the Redmi 7 is older and has a smaller cell than the Redmi 8.
A customer walked in asking for an "8 battery" and the shelf had a pack for the Redmi Note 8. Both phones are Redmi, both have an 8 in the name, yet the packs are not the same. With the Redmi 8 open, the technician read BN51 on the old cell and ordered the match. The Redmi Note 8 battery page shows what that phone uses.
Seeing BN51 before you order
On a sealed Redmi 8, BN51 cannot be seen from outside. BN51 sits under the back panel and screen frame, so its sticker appears only once a technician opens the phone. Until then, the settings and the box can only tell you which phone you hold, not which pack it has.
- Settings: open About phone to read the device name. Battery menus show the charge level but not the code.
- Retail box: the name and model number are printed on the carton label, if you still have it.
- Old battery sticker: shows BN51 with its capacity and voltage lines. Ask for a clear photo of it.
For other phones with hidden labels, our code finding guide works the same way.
BN51 capacity: 4900 rated, 5000 typical
Two numbers circulate for this pack. Redmi 8 adverts quote BN51 at 5000 mAh, the typical value. The lower 4900 mAh is the rated (minimum) value that the maker prints on the pack. A good new pack may show either, so do not treat the gap as a defect.
Watt hours for BN51 come from 5000 mAh multiplied by the printed voltage, over a thousand. If the pack sits near 3.85 V, 5000 mAh gives close to 19 Wh. Check the voltage line on your own sticker, because a pack with a similar mAh but another voltage rating holds a slightly different amount of energy.
BN51's size does not promise a fixed Redmi 8 screen time. Signal, brightness, apps and the cell's age all change it. A Redmi 8 with a healthy BN51 usually lasts a full day, while a worn one may fade by afternoon.
Signs the Redmi 8 battery is worn out
| Redmi 8 symptom | What drives it | BN51 step |
|---|---|---|
| Percentage falls fast after midday | BN51 holds far less than it did | Check Redmi 8 health, then budget for BN51 |
| Redmi 8A dies early, near a fifth charge | BN51 sags when the 8A works hard | A Xiaomi counter can load test BN51 |
| Redmi 8 back or screen edge lifting | BN51 has swollen | Unplug the Redmi 8A and go today |
| Charging stops or restarts again and again | Faulty cable, port or pack | Try another cable, then get the port checked |
For a Redmi 8, start with apps and reception on our drain causes page, and only then suspect BN51. Then the health steps help you judge BN51.
Bulging, heat, leaks or dents make BN51 a fire risk. Unplug the Redmi 8 at once, do not squeeze or poke it, and rest it on bare tile or stone away from heat. Look out for copies that print an inflated capacity, as such packs are common. Fit only a pack with the exact BN51 code.
Changing the battery of a Redmi 8
The Redmi 8 has a sealed body, and the pack is held under the back and the frame. Xiaomi service or a repairer you trust should open the Redmi 8. Give them the device name and ask them to compare BN51 with the old cell before ordering.
Inspect a new BN51 closely for signs of a weak copy:
- It is much lighter than the old BN51.
- The BN51 print is blurred and carries no batch line.
- Its label boasts well over 5000 mAh in a Redmi 8 sized shell, which no honest cell manages.
Our battery swap guide walks through fitting on a Redmi 8.
Have the shop keep the old BN51 in view until its replacement has passed a test. If the phone then charges and holds a level, the swap is done right.
Care that keeps the Redmi 8 pack healthy
The Redmi 8 family is often used for years, so the pack ages with daily habits. Heat is the main enemy. While the Redmi 8 charges, keep it away from beds, hot cars and sunshine, and peel off a thick case when it warms.
Use the Redmi 8's 10 W boxed adapter or a similar one, and replace a cable whose plug heats. Staying at full charge all night wears a cell faster, so unplug when you can. If a reboot and full charge leave the Redmi 8 still dying early, BN51 is the most likely culprit. Compare other Xiaomi phones in our Xiaomi code hub.
Frequently asked questions
Which battery code does the Redmi 8 use?
Most listings give BN51 for the Redmi 8, with 5000 mAh typical and 4900 mAh rated. Confirm it on the sticker of your old pack before ordering.
Does the Redmi 8A use the same battery code as the Redmi 8?
Most listings give the Redmi 8A and 8A Dual the same BN51 pack. Variants can differ, so a technician should read the code with the back open.
Is there a Mi 8A battery model name?
There is no phone called Mi 8A. People usually mean the Redmi 8A, which uses BN51 according to most listings. The older Mi 8 differs and takes another cell.
What capacity is the Redmi 8 battery?
Redmi 8 adverts quote 5000 mAh, the typical value. The rated minimum is 4900 mAh. Your own label shows which one the maker printed.
Can I use a Redmi Note 8 battery in a Redmi 8?
No. The Redmi 7 and Redmi 8 are different phones with different cells and codes. Even if the size looks close, a pack that does not carry BN51 may not fit or connect.
Should I swap the Redmi 8 battery at home?
Not recommended. The Redmi 8 is sealed and BN51 is fixed in place, so prying can damage it. Use Xiaomi service or a trusted shop.