Xiaomi Redmi 3 BM47 Replacement Battery 3.85V 3900mAh

Xiaomi Redmi 3 — 3.85V Li-Polymer Replacement Battery (BM47)

This is a 3900mAh (15.02Wh) 3.85V lithium-polymer cell built to replace the BM47 in the Xiaomi Redmi 3 and Redmi 3S. It fits the 5.0-inch Redmi 3 chassis directly, restoring the phone's ability to hold a charge when the original cell has degraded. Voltage and capacity match the OEM spec.

• Redmi 3 and 3S compatibility: These models share the same 3.85V power rail, BM47 connector footprint, and BMS handshake protocol. The same cell fits all variants in this lineup without modification.
• Bench tested on actual hardware: We cycled this cell through full discharge and charge on a Redmi 3 unit. The BMS accepted charge handshake on the first cycle, and protection circuits tripped correctly at both ends of the voltage window.
• Fuel gauge recalibration on first install: 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 pushes current into an uncalibrated cell.

Sudden shutdown at 20–30% on a replacement BM47 cell

This happens because the fuel gauge IC on the Redmi 3 was calibrated to the old, degraded cell's discharge curve. When the modem fires a high-current burst or the screen brightness peaks, the new cell's actual voltage drops below what the fuel gauge expects at that percentage. The phone reads this as a critical low-voltage condition and cuts power to protect the board. One full uninterrupted discharge down to automatic shutdown, followed by a complete charge to 100%, resets the coulomb counter and clears the mismatch. After that cycle, reported percentage should track actual cell voltage correctly.

USB fast charge not activating after cell replacement

On the first charge cycle after a cell swap, the Redmi 3's charge IC sometimes refuses to negotiate fast charge with the new BMS, falling back to standard 5V input instead. This is a one-time handshake issue — the charge IC runs a safety check against an unfamiliar BMS signature and defaults to slow charge. Unplug the cable, wait 10 seconds, and reconnect using the original Xiaomi charger. If fast charge still does not activate, complete one full standard charge cycle first; the IC typically accepts the fast charge protocol on the second cycle once the BMS has completed its initial calibration pass.