The BS1 battery model name, properly written B-S1, is listed for the Vivo Y21, Vivo Y21s and Vivo Y33s. Sellers list B-S1 as a 5000 mAh typical polymer pack near 3.87 V, about 19.35 Wh. The maker group is Vivo, and iQOO phones share the same B-plus-two-characters style of code. Some listings also add a Y31s 5G to the list, but that match is not settled, so treat it as something to check on the label.
People type B-S1 in many ways: BS1, B S1, B-S1 or "vivo bs1". Every spelling means the same pack. Do not confuse it with the Vivo S1 phone, which is a different handset with its own battery. The B-S1 code is on the cell sticker, so the Y21 must be opened to see it.
Quick facts
Step by step
Note the handset name and its model number
Open Settings and look under About phone. Write down the phone name and the model number. Menu names vary, so if you cannot find it, type model in the Settings search bar.
Have the old pack read at the counter
With the back panel removed by the technician, find
B-S1on the sticker, along with the capacity and voltage lines. Do not pull at the pack yourself.Compare the new pack against the old one
Put both packs side by side. The code, the size of the pack and the shape of the connector should all agree.
Judge print quality and weight
Good print is sharp and has batch marks. A pack that feels much lighter than the old one, yet claims more mAh, should be refused.
Which phones use the BS1 battery model name (B-S1)
The letter B and a hyphen mark a Vivo or iQOO pack, but the two characters after it decide the phone. For B-S1, most replacement listings match three phones. The Vivo Y21 and Vivo Y21s appear together in them, and the Vivo Y33s appears alongside in most.
| vivo Y phone | Status | Note |
|---|---|---|
| Vivo Y21 | Listed for the Y21 | 5000 mAh typical, about 3.87 V |
| Vivo Y21s | Matched by listings | Shares the Y21's B-S1 in listings |
| Vivo Y33s | Listed by most B-S1 sellers | Check the old B-S1 sticker |
| Vivo Y31s 5G | Not settled | Seen in one listing only |
| Vivo S1 (phone) | Different battery | Not a B-S1 phone |
Each phone has its own page: see the Vivo Y21 battery page and the Vivo Y33s battery page. Whatever a list says, the code you can see on the pack settles it.
Y21 and Y21s: two phones, one pack in the listings
The Y21 and Y21s look alike, and the model numbers in the listings sit very close together. This is why sellers write them in one line. Both are said to take the same B-S1 pack, so a technician who stocks one pack can serve both phones.
The catch is the long Vivo Y range. Y21 has many cousins with similar names, such as the Y21T and the Y21e, and their batteries are not confirmed as B-S1. Match the Y21 or Y33s model number from About phone before accepting any pack.
A customer came in with a Y21s whose battery lasted half a day. The counter first offered a pack for a Y20, because the name looked close. Opening the Y21, the technician saw B-S1 on the original sticker and ordered that exact part.
What 5000 mAh typical means for this pack
Y21 spec sheets quote B-S1 at 5000 mAh typical, and vivo labels often add a lower rated number. No rated B-S1 value is confirmed, so read the cell.
B-S1 energy: 5000 mAh times 3.87 V, divided by a thousand. That is 19.35 Wh for B-S1. One listing shows 3.85 V instead, so a small difference between batches is possible. Never judge two packs by mAh alone.
A Y21 or Y33s day depends on brightness, signal and apps as well as B-S1's capacity. Charge speed depends on the boxed charger's wattage. A worn pack will not reach the full 5000 mAh even when the label says so.
Codes that cause wrong B-S1 orders
Short Vivo codes are easy to misread, since S, 5 and 8 can look similar under bad light. The nearest cousin is B-S2. Some listings put B-S1 and B-S2 on the same line for the Y33s, so it is not clear whether they are one pack or two. Do not treat them as interchangeable until the old sticker says so.
- B-S7 shares the B and S but serves its own phones.
- B-O5 is the code people often mistype as B05, and it is not the same pack.
- The Vivo S1 is a phone name. Searching for "bs1" can lead you there by mistake.
For every Vivo code in one place, open the hub page for all Vivo and iQOO codes.
Signs the pack in your Y21 or Y33s is weak
| Y21 sign | Cause behind it | Next step for B-S1 |
|---|---|---|
| Y21 percentage drops in jumps | Aged B-S1 with low real capacity | Run a battery check, then plan a swap |
| Y21 dies at 15 to 25 percent | B-S1 cannot give peak current | Have B-S1 tested at a service counter |
| Y33s screen lifts or back gaps | B-S1 has puffed up | Unplug the Y33s and go today |
| Y21 warm at rest | Worn B-S1 or a stuck app | Restart the Y21, remove its case, get B-S1 checked |
On the Y21, rule out heavy apps and patchy reception using our page on drain. Then the health steps show whether B-S1 really needs replacing.
Should B-S1 bulge, heat up, leak or dent, it may ignite. Unplug the Y21, leave it alone rather than squeezing it, and keep heat away. B-S1 copies often claim far beyond 5000 mAh, so only a pack printed B-S1 will do.
Fitting a new B-S1 pack without trouble
The Y21 and Y33s are sealed, so trained hands should open them. A brand service centre is the safest route, and a trusted repair counter is the second choice. Tell them the exact handset and its model number and request a comparison of B-S1 with the old pack before anything is glued back.
Spotting a poor copy is not hard if you look closely:
- It is clearly lighter than the B-S1 that came out.
- B-S1 print is smudged with no batch detail.
- It boasts 6000 mAh or more in a Y21 sized shell. No honest cell of B-S1's size could store that.
Fitting on any phone is covered in our replacement guide.
Before the old B-S1 is binned, ask to photograph its print under bright light. If the code is needed again, you will already have it.
Everyday care for a 5000 mAh Vivo Y pack
Y21 owners often charge overnight, and that habit plus heat wears B-S1 faster than normal use. Avoid charging the Y33s on a bed, in a hot car or in sun. A thick case that traps heat is worth removing while the phone charges.
Charge the Y21 with its boxed adapter and cable or something rated no higher. If a plug end turns hot, change that cable. Unplug when the phone is near full if you can. Before you buy, test B-S1 if the Y21 or Y33s keeps cutting out after a reboot and full charge.
Frequently asked questions
Which vivo phones use B-S1?
Sellers mostly tie B-S1 to the vivo Y21, Y21s and Y33s, at 5000 mAh typical. Check the code on the old cell before you order.
Is B-S1 the Vivo Y21 battery model name?
Replacement listings give B-S1 for the Y21. Once the Y21's back is off, B-S1 can be read straight from the cell.
Is the Vivo S1 battery the same as B-S1?
No. The Vivo S1 is a phone with its own battery. B-S1 is a code, and it is listed for the Y21, Y21s and Y33s.
How many mAh is the B-S1 battery?
Sellers give B-S1 5000 mAh typical. B-S1's rated minimum may sit just below that; your label shows it.
Will a B-S2 work in place of B-S1?
Do not assume it. Some listings group the two codes, but that does not prove they are the same. Match the full B-S1 code and plug.
How can I spot a fake B-S1 battery?
B-S1 fakes weigh less, look blurry, lack batch marks and promise past 5000 mAh. Hold the new B-S1 against the original and weigh both.