Xiaomi Mi 5s Plus BM37 Replacement Battery 3.8V 3800mAh

Xiaomi Mi 5s Plus ( China Version ) — 3.8V Li-Polymer Replacement Battery (BM37)

The BM37 is a 3.8V, 3800mAh lithium-polymer cell that fits the Xiaomi Mi 5s Plus (China Version) and Mi 5s Plus Premium Edition (China Version). It replaces the original pack when the existing cell has degraded, swells, or no longer holds a usable charge. Capacity figures are taken directly from the product specification — 3800mAh at 14.44Wh.

• Mi 5s Plus and Premium Edition compatibility: Both variants use the same BM37 cell footprint, connector pinout, and BMS handshake protocol. The 77.68 × 64.75 × 4.10 mm dimensions match the chassis cavity on both builds, and the fuel gauge IC on each board reads the same cell identification data.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Mi 5s Plus board. The BMS accepted the pack without error flags, the charge IC engaged correctly, and coulomb counter readings tracked consistently across three full cycles.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging for one complete discharge-to-charge cycle. The fuel gauge IC on the Mi 5s Plus is calibrated to the old cell's discharge curve — running one slow cycle first lets it map the new curve before high-current charging begins.

Sudden shutdown at 20–30% on the replacement BM37 cell

The Mi 5s Plus uses a dual-camera setup and a Snapdragon 821 SoC — both spike current draw hard during camera bursts and LTE handoffs. A new cell with an uncalibrated fuel gauge IC may report 25% charge while actual cell voltage has already dipped below the BMS cutoff threshold under that load spike. The phone shuts down to protect the cell, even though the displayed percentage looked safe. One full discharge-charge cycle without fast charging forces the coulomb counter to anchor its zero-point to the real cell floor — shutdowns typically stop after that recalibration pass.

Phone shows wrong battery percentage after BM37 swap

The fuel gauge IC on the Mi 5s Plus stores a learned discharge curve from the previous cell. When a new BM37 goes in, the IC has no reference data for its specific internal resistance or voltage slope, so percentage readings drift or jump — often reading 100% immediately after fitting, or dropping 10% in seconds. This is not a fault with the replacement cell; it is the IC recalibrating. Drain the battery fully until the phone powers off on its own, then charge uninterrupted to 100% using the stock charger at standard 5V/2A — one complete cycle resets the curve.