Xiaomi Redmi Note 5 Compatible Battery BN45 3.85V 3900mAh

Xiaomi Redmi Note 5 — 3.85V Li-Polymer Replacement Battery (BN45)

This is a 3.85V, 3900mAh lithium-polymer cell built to the BN45 specification. It fits the Redmi Note 5, Redmi Note 5 Standard Edition Global, and the Dual SIM TD-LTE variant, among other MEG7S-series models. Swap it when the original cell can no longer hold enough charge to get through a normal day.

• Redmi Note 5 series fit: All listed variants share the same physical footprint, connector pinout, and BMS handshake protocol — the fuel gauge IC on every board in this family reads the same cell chemistry signature, so no firmware flags are triggered on swap.
• Bench tested on actual hardware: We cycled this cell through charge and load on a Redmi Note 5 board. The BMS accepted the cell without lockout, the charge IC ramped current correctly, and the coulomb counter began tracking within one full discharge cycle.
• First-cycle fuel gauge recalibration: After installation, disable fast charging and run one full discharge down to auto-shutdown, then charge slowly to 100%. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging begins on an uncalibrated cell.

Why the Redmi Note 5 reports wrong battery percentage after a cell swap

The fuel gauge IC stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches the actual voltage-to-capacity relationship of the replacement. The IC reads voltage correctly but maps it to the wrong capacity figure, so the percentage display drifts. One full discharge-to-shutdown followed by a slow charge to 100% forces the coulomb counter to re-anchor to the new cell's curve.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops sharply under combined modem and display load — a voltage cliff the fuel gauge did not predict because its curve was calibrated to the old cell. The phone's protection circuit reads the drop as an imminent under-voltage event and shuts down before the displayed percentage reaches zero. Run the recalibration cycle first: one slow full discharge, then charge uninterrupted to 100%. If shutdowns continue after two full cycles, check that the cell resting voltage reads above 3.7V with a multimeter before reinstalling.