Redmi BN47 6 Pro Replacement Battery 3.85V 3900mAh

Redmi 6 Pro / M1805D1SE — 3.85V Li-Polymer Replacement Battery (BN47)

This is a 3900mAh Li-Polymer cell rated at 3.85V (15.02Wh), built to replace the OEM BN47 battery in the Redmi 6 Pro and 6 Pro Premium Edition Dual SIM. It fits the M1805D1SE, M1805D1SC, and related model variants. If your phone no longer holds charge through a normal day, this cell restores capacity without replacing the handset.

• 6 Pro model family compatibility: The M1805D series shares the same battery bay dimensions, connector pinout, and BMS handshake protocol. All listed variants accept the BN47 form factor — 81.62 × 62.45 × 4.26mm — without any physical modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Redmi 6 Pro platform. The BMS accepted the cell without error flags, thermal cutoff held within normal bounds, and the charge IC communicated correctly throughout the test cycle.
• First-cycle fuel gauge reset: After installation, disable fast charging and run one full discharge down to automatic shutdown, then charge uninterrupted to 100%. This lets the fuel gauge IC map the new cell's discharge curve before fast-charge current is applied to an uncalibrated cell.

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

The fuel gauge IC on the Redmi 6 Pro uses a coulomb counter that was calibrated against the discharge curve of the original, degraded cell. When a fresh 3900mAh cell goes in, the IC has no reference for the new cell's voltage-to-capacity relationship. It will over- or under-report percentage until it learns the curve. One complete discharge-charge cycle without interruption corrects this — the IC re-anchors its endpoints at 0% and 100% against the actual cell behaviour.

Sudden shutdown at 20–30% on a replacement cell

This happens when the modem, screen, or processor pulls a short burst of high current and the battery voltage drops below the BMS cutoff threshold — even though the displayed percentage looks safe. On a freshly installed cell with an uncalibrated fuel gauge, the IC has not yet learned where the voltage cliff actually sits. The phone cuts out because the BMS sees voltage fall below approximately 3.2V under load, not because the cell is empty. Run one full calibration cycle first, then check whether shutdowns continue — if they persist past that, verify the replacement cell seated fully against the connector.