The BM4Y battery model name is given by spare part listings for the POCO F3 and the Redmi K40, both Xiaomi group phones. The pack is listed at 4520 mAh typical. BM4Y starts with BM, a Xiaomi prefix on many Redmi, Mi and POCO cells, though BM alone never names the phone. The phone list is what matters.
People also search this as "mi bm4y battery model name". The POCO F3 and the Redmi K40 are close relatives sold under different names in different countries, and the model numbers differ by a letter or two. The Mi 11X and Mi 11i are sold in India too, but their battery code is not confirmed here. So the number on your box or in your settings is a better guide than the marketing name. Where the sources do not agree, this page says so and tells you what to check.
Quick facts
Step by step
Write down the phone name and model number
Open Settings, tap About phone and note the device name and model number. If you cannot see the number, type model in the Settings search bar.
Compare it with the box
The retail box carries a model number too. Both should agree. Listings for BM4Y mention model numbers that begin with M2012K11, so a number from another series is a reason to stop and check.
Get the old cell read after the back is opened
On this glass-back phone only a technician should lift the cover. The sticker on the cell shows
BM4Ybeside the capacity and voltage.Place old and new packs side by side
Look at the code, the connector, the outline and the thickness. A different shape is a clear sign of the wrong pack, even when mAh is equal.
Test the new pack before you leave
Have the phone switched on at the counter. Check that it boots, charges and shows a sensible percentage on the screen.
Phones that use the BM4Y battery model name
Listings for BM4Y name the POCO F3 with model number M2012K11AG and the Redmi K40. The POCO F3 and Redmi K40 are one design under two names, which fits a shared BM4Y. Parts listings, not Xiaomi's own catalogue, back this match, so treat the table as a lead and the old label as final.
| POCO or Redmi handset | Model number | Status |
|---|---|---|
| POCO F3 | M2012K11AG | Named by listings |
| Redmi K40 | Not confirmed | Named by listings; sold mainly outside India |
| Mi 11X | Not confirmed | Looks related to the POCO F3, but not confirmed |
| Mi 11i | Not confirmed | Listings disagree, so check the label |
Some phones in this family came in versions with different model numbers for different regions. Always give the repair shop your own model number, because a pack bought for another version may carry a different code.
How to confirm BM4Y before you order a replacement
Never order BM4Y on the POCO F3 name alone. Three quick checks save a wasted trip: the model number in About phone, the box, and the old cell read with the back open. The code you want is the one on the cell, not the one in a search result.
A customer came in with a phone sold as a Mi model and asked for a POCO F3 battery, because both names appeared in an online listing. With the POCO F3 open, the technician found BM4Y on the old cell, a match. Had it shown another code, the order would have been cancelled before payment.
If you cannot visit a technician first, ask the seller for a clear picture of the label of the pack you will receive, with the code readable. A pack shown only in a stock image proves nothing. Our label reading guide covers codes on any phone.
BM4Y 4520 mAh: typical, rated and watt hours
POCO F3 adverts quote BM4Y's 4520 mAh as the typical figure. Xiaomi usually prints a slightly lower rated minimum on BM4Y. This page does not quote that figure for BM4Y, since it was not confirmed. Your own label will show it, and it can differ a little from batch to batch.
BM4Y energy: multiply mAh by volts and divide by 1000. BM4Y at 3.87 V holds roughly 17.5 Wh. If it shows a different voltage, use that one. A K40 pack at another voltage would hold different energy, so never compare mAh alone.
A POCO F3's endurance hinges on its chip, 120 Hz panel, brightness, reception and apps. POCO F3 charge speed depends on its 33 W charger and cable. A fresh pack gives you the maker's design life, not extra hours beyond it.
Look-alike codes at the repair counter
BM4Y sits in a crowded family. A single changed letter or digit usually means a different phone, a different size and a different connector.
BM4Wis close in spelling. It has its own phones, so open BM4W and compare lists before accepting a pack with that mark.BM5RandBN5Rare also near neighbours on the shelf. See BM5R and BN5R for what they power.BP4Kis another one printed in a similar style. Its page is BP4K.
The letters Y, V and W can look alike when print is faint, so tilt the sticker under bright light. All Xiaomi group codes are gathered on our Xiaomi code hub.
When a BM4Y pack is wearing out
| POCO F3 symptom | Likely reason | Next step for BM4Y |
|---|---|---|
| F3 percentage drops in jumps | Aged BM4Y with lost capacity | Check POCO F3 health, then plan a BM4Y |
| K40 dies showing 15 to 30 percent | Tired BM4Y under heavy load | Restart, test, then change the pack |
| POCO F3 screen lifts or back gaps | BM4Y has swollen | Stop using the F3 and see a repairer today |
| Phone is hot while idle | A rogue app, poor signal or worn BM4Y | Close apps, remove the cover, get it checked |
Fast drain does not always mean a bad pack. Begin with our page on drain causes, then a health check shows how much BM4Y has left.
A pack that bulges, turns very hot, leaks or gets dented can catch fire. Pull the plug on the POCO F3, put it down on a hard surface away from anything that could catch, and leave the cell unpressed. Then take the POCO F3 to Xiaomi service. Inflated BM4Y fakes are common; only the exact code with a believable label is acceptable.
Fitting a new pack in a glass-back phone
Adhesive and a glass back seal the POCO F3 and K40, so opening them takes heat, tools and patience. Leave the F3 to Xiaomi service or a well regarded shop. An untrained attempt can crack the glass or cut the flex cable that sits near the cell.
Check these points when a new BM4Y is shown to you:
- It weighs close to the old BM4Y, not clearly less.
- The print is crisp, with batch details and the code
BM4Yspelled in full. - The stated mAh is near 4520. A figure far above that for a cell of this size is not believable.
Our fitting guide has more general advice.
Ask for the old BM4Y back and photograph its sticker. If the new one fails early, the code and batch of both packs are on record.
Everyday care for a 4520 mAh pack
Heat harms BM4Y more than anything else. Gaming while the phone charges, leaving it on a car dashboard or sleeping with it under a pillow all push the cell temperature up and shorten its life. Remove a thick case if the POCO F3 warms during long gaming sessions.
Charge the POCO F3 from its boxed brick or a dependable equal, and retire any cable warming at the plug. Nightly hours at 100 percent also wear BM4Y, so unplug when you can. Persistent early shutdowns on the POCO F3 after a reboot and full charge mean BM4Y needs testing before you buy.
Frequently asked questions
Which phone uses the BM4Y battery?
Spare part listings match BM4Y to the POCO F3 and the Redmi K40, with a typical capacity of 4520 mAh. Read your old cell's label to be sure, especially on other Xiaomi phones of that period.
Is BM4Y the POCO F3 battery model name?
Yes, according to the listings seen. The POCO F3 is given with model number M2012K11AG. With the back open, a technician can confirm BM4Y.
How many mAh is the BM4Y battery?
It is listed at 4520 mAh typical. BM4Y may print a rated minimum slightly below 4520 mAh.
Can I use a BM4W or BM5R battery instead of BM4Y?
Do not assume it will fit. A different code usually means a different phone, shape or connector. Compare the full BM4Y code and plug before fitting.
Is the Mi 11i battery the same as BM4Y?
Listings disagree there, so it stays unconfirmed. Read the code on that phone's own cell before ordering. The same goes for the Mi 11X, which looks related to the POCO F3.
How can I spot a fake BM4Y battery?
Counterfeit BM4Y packs feel lighter, smudge, skip batch marks and promise beyond 4520 mAh. Compare weight and BM4Y code with the old cell.