Redmi BM46 Replacement Battery 3.8V 3900mAh Li-Polymer

Redmi BM46 — 3.8V Li-Polymer Replacement Battery (BM46)

The BM46 is a 3.8V, 3900mAh (14.82Wh) Li-Polymer cell that replaces the factory battery in Redmi smartphones carrying the BM46 part number. It fits the physical footprint at 74.61 × 60.20 × 5.60mm and connects via the original flex cable and BMS harness. If your phone shuts down early, charges slowly, or swells, this cell is the direct swap.

• BM46 platform fit: Redmi devices on the BM46 platform share the same connector pinout, voltage rail, and BMS handshake. The replacement cell matches the original discharge curve so the fuel gauge IC can track capacity without misreporting state-of-charge.
• Bench tested on actual hardware: We cycled this cell through charge, load, and cutoff on BM46-compatible hardware. The BMS accepted the cell without a protection trip, and the coulomb counter initialised correctly on the first full discharge cycle.
• 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 pushes into an uncalibrated state-of-charge window.

Sudden shutdown at 20–30% on the replacement cell

A fresh BM46 cell has a steeper voltage cliff than a broken-in cell under modem or screen load. When the phone demands a current spike — LTE handoff, display brightness jump — the cell voltage dips below the BMS cutoff threshold before the reported percentage reaches zero. The fuel gauge IC hasn't yet mapped the new cell's internal resistance, so it reads capacity optimistically. Run one full discharge to 0% and a full charge to 100% without interruption; the coulomb counter resets its reference and the early shutdowns stop.

Phone feels warm near the battery on the first few charges

A new Li-Polymer cell comes with slightly higher internal impedance than a cell that has been cycled. The charge IC compensates by pushing a higher voltage differential across that impedance, which generates heat at the cell surface. This is normal for the first two to three cycles as the electrolyte settles and impedance drops. If the phone stays warm past the fifth charge, check that the battery flex connector is fully seated — a partial connection increases contact resistance and keeps impedance elevated.