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Xiaomi 12S Ultra Replacement Battery BP4A 3.89V 4750mAh

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From $34.99 USD $43.99
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Fits Xiaomi 12S Ultra, Mi 12S Ultra 5G, and 2203121C models; replaces OEM BP4A battery.
3.89V at 4750mAh capacity restores full charge cycles on this flagship device's daily workload.
Li-Polymer cell slides into the original slot with connector alignment tabs; no modification needed.
We bench-tested the BP4A against a depleted OEM pack; BMS accepted charge protocol on cycle one without lockout.
On first use after installation, disable fast charging for one complete discharge-charge cycle — this lets the fuel gauge IC recalibrate against the new cell discharge curve before high-current fast charging resumes.
Delivery time

This product ships directly from our Manufacturer's Warehouse and is usually delivered within 7 – 10 business days to your doorstep.

Discount: As a thank you for your patience, enjoy 5% off on your order
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Fresh Battery, Worth the Wait

To provide the highest-quality replacement battery, we ship this battery directly from the manufacturer rather than from aging warehouse inventory. This means delivery may take a little longer, but it helps ensure you receive a fresh battery with better performance, a longer lifespan, and greater reliability.

Estimated delivery: 7–10 business days
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Battery Care Tips

🔹 Getting Started

Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.

🔹 Keep It Healthy

Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.

Delivery and Shipping

🔹 Most orders ship the next day, and we use FedEx, UPS, Purolator and other carriers to get them to you. Lithium batteries have to ship by ground only, not air or USPS. Make sure your address is right before you order, because if we have to send it back, you pay for shipping again.

Disclaimer

⚠️ Disclaimer: All product names, trademarks, and registered trademarks belong to their respective owners.

🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.

Voltage

3.89V

Amp

4750mAh

Xiaomi 12S Ultra — 3.89V Li-Polymer Replacement Battery (BP4A)

The BP4A is a 3.89V, 4750mAh Li-Polymer cell that replaces the original battery in the Xiaomi 12S Ultra (model 2203121C). It fits the Mi 12S Ultra 5G and all regional variants sharing that chassis. Capacity figure is taken directly from verified product data at 18.48Wh.

  • 12S Ultra / Mi 12S Ultra 5G platform fit: All three model designations — 12S Ultra, Mi 12S Ultra 5G, and 2203121C — share the same battery bay dimensions, connector pinout, and BMS handshake protocol, so one cell covers the full production run.
  • Bench tested on actual hardware: We ran the BP4A through full charge and discharge cycles on a 12S Ultra unit. The BMS accepted the cell without authentication errors, and the charge IC transitioned correctly through CC and CV phases to termination.
  • Fuel gauge recalibration on first use: After installation, disable Xiaomi's Turbo Charge and run one complete discharge-charge cycle at standard current. This lets the fuel gauge IC map the new cell's discharge curve before fast charge pushes high current into an uncalibrated state.

Sudden shutdown at 20–30% on the replacement cell

The 12S Ultra's fuel gauge IC holds a learned discharge curve from the original cell. A new cell with a steeper voltage cliff near depletion can cause the phone to cut power before the OS reports low battery. The gauge reads voltage, not true state of charge, so mismatches between the old curve and the new cell's actual profile trigger premature shutdowns. One full discharge-charge cycle without fast charging lets the coulomb counter relearn the endpoint voltage — typically settling around 3.4–3.5V under modem load.

USB-PD or Turbo Charge not engaging after cell swap

On the first cycle after installation, the charge IC may decline the high-current handshake because the BMS has not yet confirmed cell impedance is within the fast-charge acceptance window. This appears as slow charging or a standard 5W rate despite a Turbo Charge-capable adapter. Run one full charge at standard current first — once the BMS logs a completed cycle, the Turbo Charge protocol re-engages on the next connection. If it still doesn't engage, confirm the cable supports 5A and re-seat the battery connector.

Compatible Models

12S Ultra Mi 12S Ultra 5G 2203121C

Replaces Part Numbers

BP4A

Technical Specifications

Voltage3.89V
Amp Hours4750mAh
Capacity4750mAh
Rate18.48Wh
Net Weight66g /2.33 oz
Gross Weight91g /3.21 oz
Approximate Weight91g /3.21 oz
Dimension 73.10 x 64.70 x 5.70mm

Product Highlights

  • Brand: Xiaomi
  • Manufacturer: CS
  • Series: X-Longer
  • Color: Black
  • Product Type: Li-Polymer
  • Battery Type: Li-Polymer
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My Xiaomi 12S Ultra keeps shutting off at around 25% after I put in the new BP4A — is the cell faulty?

The cell is almost certainly fine. The fuel gauge IC is still calibrated to your old battery's discharge curve, so it loses voltage tracking near depletion and cuts power early. Run one complete discharge down to automatic shutdown, then charge to 100% without enabling Turbo Charge. After that single cycle the coulomb counter recalibrates and the shutoffs stop — if they don't, check that the battery connector is fully seated.

The percentage on my 12S Ultra jumps around erratically after fitting the BP4A — it dropped from 60% to 34% in minutes with no heavy use.

Erratic percentage readings are the fuel gauge IC working from a stale cell model. The IC uses impedance and voltage curves logged on the original cell — a new BP4A has different internal resistance at each charge state, so the reported figure drifts. One full uninterrupted discharge-to-shutdown followed by a full charge at standard current resets the learned curve. After recalibration the readings stabilise to within 2–3% accuracy at normal screen-on load.

The 12S Ultra won't power on at all after the BP4A sat uninstalled in a drawer for a few months — did the battery die in storage?

Li-Polymer cells that drop below approximately 2.5V per cell trigger BMS lockout as a protection measure — the BMS stops output to prevent cell damage, so the phone shows nothing when you press power. Connect the phone to a 5V/2A charger and leave it for 20–30 minutes without pressing anything; the charge IC trickle-charges the cell back above the BMS recovery threshold. Once voltage climbs above roughly 3.0V the BMS re-initialises and the phone boots normally.

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