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Xiaomi Redmi 6A Replacement Battery BN37 3.85V 2900mAh

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From $24.99 USD $30.99
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Fits Xiaomi Redmi 6A and replaces OEM battery BN37 across all regional variants.
3.85V lithium-polymer cell delivers 2900mAh capacity — sustains the Redmi 6A's modem, display, and radios through a full day without sag.
Connector slides straight into the factory socket with standard polarity — no tab rotation needed; locking catch on the right side seats flush.
We cycled this cell on a Redmi 6A test unit; the BMS accepted charge without protection fault, and discharge held voltage steady through 50% capacity.
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 curve before high-current charging.
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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

3.85V

Amp

2900mAh

Xiaomi Redmi 6A — 3.85V Li-Polymer Replacement Battery (BN37)

The BN37 is a 3.85V, 2900mAh Li-Polymer cell that fits the Xiaomi Redmi 6A and Redmi 6A Dual SIM TD-LTE, including variants M1804C3DH and M1804C3DC. It replaces a degraded original cell when the phone no longer holds a charge or shuts down unexpectedly under load. Capacity matches the factory specification at 11.17Wh.

  • Redmi 6A platform fit: The M1804C3 hardware family shares a single battery bay, connector pinout, and BMS handshake across all Redmi 6A variants. The BN37 slot and NTC thermistor pin position are consistent across these builds, so one cell covers the full model range listed.
  • Bench tested on actual hardware: We cycled this cell on a Redmi 6A unit and confirmed the BMS accepted charge at both standard and fast-charge rates. The protection circuit tripped correctly at low-voltage cutoff, and charge termination occurred cleanly at full capacity.
  • Fuel gauge recalibration on first use: After installation, disable fast charging and run one full discharge-charge cycle at the standard rate. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging pushes current into an uncalibrated measurement window.

Why the Redmi 6A reports wrong battery percentage after a cell swap

The Redmi 6A uses a coulomb-counter fuel gauge IC that stores a discharge curve calibrated to the original cell. When a new cell goes in, the stored curve no longer matches the actual voltage-versus-capacity profile of the replacement. The gauge reads the new cell's voltage and maps it against old data, producing percentage figures that jump or plateau. One complete slow discharge from 100% to shutdown — followed by a full charge — resets the calibration baseline and the percentage display stabilises.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC has not yet recalibrated and the cell voltage drops below the modem or display load threshold faster than the displayed percentage predicts. The phone's BMS issues a hard cutoff to protect the cell, even though the screen shows charge remaining. It is not a faulty battery — it is a calibration mismatch. Complete one full discharge-charge cycle at standard rate; after recalibration, the cutoff should align with a displayed level below 5%.

Compatible Models

Redmi 6A Redmi 6A Dual SIM TD-LTE M1804C3DH M1804C3DC M1804C3DE Cereus M1804C3CC M1804C3CE M1804C3CT M1804C3DT

Replaces Part Numbers

BN37

Technical Specifications

Voltage3.85V
Amp Hours2900mAh
Capacity2900mAh
Rate11.17Wh
Net Weight39.2g /1.38 oz
Gross Weight64g /2.26 oz
Approximate Weight64g /2.26 oz
Dimension 74.10 x 59.40 x 3.60mm

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 Redmi 6A won't turn on after the new BN37 battery sat in a drawer for a few months — what's happening?

A Li-Polymer cell left uncharged for an extended period can drop below 2.5V, which triggers BMS lockout to prevent cell damage. The phone will not respond to the power button because the BMS is blocking current to the board. Connect the phone to a charger and leave it for 15–20 minutes without pressing anything — the charge IC will trickle current into the cell until it clears the lockout threshold, after which normal charging resumes. If the charging indicator does not appear after 30 minutes, check the cable and adapter, then retry at a wall socket rather than a USB port.

Fast charging stopped working after I fitted the BN37 — the phone only charges slowly now.

On the first cycle after installation, the Redmi 6A's charge IC can fail to complete the USB proprietary protocol handshake with a new BMS, defaulting to standard 5V charging instead. This is not a fault in the cell — it is the device's charge controller being cautious with an uncalibrated cell. Run one full standard charge-discharge cycle, then reconnect the original fast-charge adapter. The handshake typically completes correctly from the second cycle onward once the BMS has logged an initial charge profile.

The battery percentage on my Redmi 6A keeps jumping around erratically — it went from 45% to 71% without charging.

The coulomb-counter IC inside the Redmi 6A is still using the discharge curve it built for the old, degraded cell. When it reads voltage from a new cell with a different impedance profile, the percentage calculation produces erratic jumps. Charge the phone to 100% using a wall adapter, then allow it to discharge continuously — no top-ups — until the phone shuts itself down, then charge back to 100% uninterrupted. After that single calibration cycle, the gauge recalculates its baseline against the new cell and the percentage display should stabilise to within ±3%.

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