Xiaomi Redmi 5 BN35 Replacement Battery 3.85V 3200mAh

Xiaomi Redmi 5 — 3.85V Li-Polymer Replacement Battery (BN35)

This is a 3.85V, 3200mAh lithium-polymer cell built to the BN35 specification for the Xiaomi Redmi 5 smartphone. It replaces the original pack when the Redmi 5 suffers from rapid capacity fade, unexpected shutdowns, or a battery that no longer holds a charge. Voltage and dimensions match the original: 78.72 × 63.10 × 3.50mm.

• Redmi 5 fitment: The Redmi 5 uses a fixed connector position and a charge IC tuned to 3.85V nominal. A cell at the wrong voltage rail throws off the fuel gauge IC and triggers early cutoff — this cell matches the original voltage spec to keep the charge IC operating within its calibration window.
• Bench tested on actual hardware: We cycled the BN35 cell through charge and discharge on a Redmi 5 mainboard. The BMS accepted the cell without a handshake error, and the charge IC transitioned correctly from constant-current to constant-voltage phase at 4.35V.
• First-cycle recalibration after installation: On first use, disable fast charging and run one full discharge-to-charge cycle at standard rate. This lets the fuel gauge IC build a fresh discharge curve against the new cell before high-current charging pushes into an uncalibrated coulomb counter.

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

The Redmi 5 uses a coulomb counter that stores learned capacity data from the original cell. When a new cell goes in, that stored data no longer matches the actual discharge curve, so the percentage reading drifts — often showing 30% when the cell is nearly flat. One complete slow discharge from 100% to automatic shutoff, followed by a full charge, resets the learned values. After that cycle, percentage readings stabilise across the full voltage range of 3.0V to 4.35V.

Sudden shutdown at 20–30% on the replacement cell

This happens because the fuel gauge IC is still running the old cell's voltage-to-capacity curve. When the modem fires during a call or data burst, it pulls current the old curve didn't account for at that state of charge, voltage sags below the protection threshold, and the BMS cuts power. The phone reads 25% but the cell is already at its load voltage floor. Run one full calibration cycle — slow discharge to cutoff, then charge uninterrupted to 100% — and the IC recalculates the sag margin correctly.