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Redmi K30 Ultra 5G BM4U Replacement Battery 3.85V 4300mAh

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From $28.99 USD $35.99
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Fits Redmi K30 Ultra 5G with OEM part number BM4U replacement only.
3.85V nominal, 4300mAh capacity delivers sustained voltage for processor and display loads.
Connector seats vertically into the upper battery slot with single mechanical locking tab.
We bench-tested this cell on a K30 Ultra 5G motherboard; the BMS accepted charge immediately without fault codes.
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 charging pushes current into an uncalibrated cell.
Delivery time

This product ships directly from our Manufacturer’s Warehouse and is usually delivered within 5 – 8 business days to your doorstep.

Discount: As a thank you for your patience, enjoy 5% off on your order
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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.

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⚠️ 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

3.85V

Amp

4300mAh

Redmi K30 Ultra 5G — 3.85V Li-Polymer Replacement Battery (BM4U)

This is a 3.85V, 4300mAh (16.56Wh) Li-Polymer cell built to the BM4U specification. It fits the Redmi K30 Ultra 5G (model M2006J10C). Install this when the original cell no longer holds charge across a normal day of use.

  • K30 Ultra 5G and M2006J10C compatibility: Both model references draw from the same voltage rail and use the same BM4U connector pinout. The BMS handshake is identical across these variants, so one cell covers both.
  • Bench tested on actual hardware: We cycled this cell through charge and discharge on the K30 Ultra 5G platform. The BMS accepted charging without fault flags, and the protection circuit tripped correctly at the low-voltage cutoff threshold.
  • Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging begins pushing current into an uncalibrated cell.

Sudden shutdown at 20–30% on the replacement cell

This happens because the fuel gauge IC is still running the discharge curve from the old, degraded cell. The new cell has a steeper voltage drop under modem and display load than the IC expects at that state of charge. When the terminal voltage dips below the protection threshold during a high-draw moment, the BMS cuts power before the percentage readout reaches zero. Run one full discharge to below 5% and a full charge to 100% without interruption — this forces the coulomb counter to reset against the actual cell capacity.

USB fast charge not initiating after installation

On the first charge cycle after a cell swap, the charge IC may default to standard 5V input and refuse to negotiate the proprietary fast-charge protocol. This is a protective behaviour — the charge controller treats an unrecognised BMS state as a reason to limit current. Plug in using the original Redmi charger and cable, let the first full cycle complete at standard rate, and fast charging should negotiate correctly from the second cycle onward. If it does not, check that the battery connector is fully seated — a partial connection raises contact resistance enough to trip the protocol handshake.

Compatible Models

K30 Ultra 5G M2006J10C

Replaces Part Numbers

BM4U

Technical Specifications

Voltage3.85V
Amp Hours4300mAh
Capacity4300mAh
Rate16.56Wh
Net Weight60.8g /2.14 oz
Gross Weight110.8g /3.91 oz
Approximate Weight110.8g /3.91 oz
Dimension 77.54 x 63.70 x 5.20mm

Product Highlights

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

Frequently Asked Questions

My K30 Ultra 5G powers off at around 25% after fitting the new BM4U battery — what's causing that?

The fuel gauge IC is still calibrated to the old cell's discharge curve and misjudges where the new cell's voltage will drop under load. When the modem or display spikes current draw, the terminal voltage dips fast enough to trigger the BMS cutoff before the percentage reaches zero. Run one uninterrupted discharge down to under 5% followed by a full charge to 100% — this resets the coulomb counter against the real capacity of the new cell. After that cycle, early shutdowns typically stop.

The battery percentage on my K30 Ultra 5G jumps around erratically after the replacement — is the new cell faulty?

It is not a faulty cell. The fuel gauge IC stores a learned discharge model from the old battery, and the new cell's chemistry does not match that stored curve yet. The IC is essentially guessing between data points it was not trained on. Complete two full discharge-charge cycles without interrupting or topping up mid-cycle — the coulomb counter recalibrates on each full pass and percentage reporting stabilises by the second or third cycle.

The phone gets noticeably warm near the battery during the first few charges — is that normal with the BM4U cell?

Yes, and it is specific to the first few cycles on a fresh high-impedance cell. A new Li-Polymer cell has slightly higher internal resistance than a broken-in one, so the charge IC dissipates more heat as it pushes current through that resistance. Warmth during charging is expected; heat that makes the back panel uncomfortable to hold is not. If the device becomes hot rather than warm, disable fast charging in Settings → Battery → Charging for the first two cycles, then re-enable it — this reduces charge current until the cell's internal resistance drops to its normal operating range.

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