Redmi 6A BN37 Replacement Battery 3.85V 2900mAh

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

This is a 3.85V, 2900mAh Li-Polymer replacement battery for the Redmi 6A smartphone. It carries OEM part number BN37 and fits the M1804C3DH, M1804C3DC, and Redmi 6A Dual SIM TD-LTE variants. Install it when the original cell no longer holds a charge or the phone shuts down unexpectedly under load.

• 6A variant compatibility: The M1804C3DH and M1804C3DC share the same physical cell footprint, connector pinout, and BMS handshake requirements. One BN37 cell covers all listed variants without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a Redmi 6A unit. The BMS accepted charge at both standard and fast-charge rates after the first full calibration cycle, and protection cutoffs triggered correctly at both ends of the voltage range.
• 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 on an uncalibrated cell.

Sudden shutdown at 20–30% on the Redmi 6A after a cell swap

The Redmi 6A's fuel gauge IC stores a discharge curve calibrated to the original cell. A new cell has a different internal resistance profile, so the IC misreads the actual state of charge. When the modem fires or the screen peaks in brightness, voltage sags below what the IC expects — and the phone cuts off even though charge remains. One full discharge-to-shutdown followed by an uninterrupted charge to 100% forces the coulomb counter to reset against the new cell's actual curve. After that cycle, shutdowns at false low percentages stop.

Phone reports wrong battery percentage after BN37 installation

The MIUI fuel gauge IC on the 6A uses a learned model built from the old cell's charge history. Swapping in a new BN37 cell means that stored model no longer matches real cell behaviour, so the percentage readout drifts — often jumping several points or stalling at a fixed number. A full calibration cycle corrects this: drain the battery until the phone shuts itself off, then charge straight to 100% without interruption. After one complete cycle the IC recalibrates and percentage tracking stabilises.