About this replacement
Xiaomi Mi 5s Plus Premium Edition — 3.85V Li-Polymer Replacement Battery (BM37)
This is a 3800mAh Li-Polymer cell at 3.85V nominal, built to replace the original BM37 battery in the Xiaomi Mi 5s Plus Premium Edition and Mi 5s Plus (International Version). It fits the dual-camera flagship directly, restoring the power the phone had when new. Dimensions are 77.60 × 64.70 × 4.10mm — match these before ordering if your unit has been repaired before.
- Mi 5s Plus International fit: The BM37 is specific to the International Version variant. Domestic Chinese units use a different cell configuration. Voltage rail, connector position, and BMS handshake on the International board all match this cell exactly.
- Bench tested on actual hardware: We ran this cell on a Mi 5s Plus International board and confirmed BMS communication, charge acceptance across a full cycle, and stable cutoff at both ends of the voltage window. No false full-charge flags on the first cycle.
- First-cycle fast charge lockout: On first use after installation, disable fast charging for one full discharge-charge cycle. The fuel gauge IC on the Mi 5s Plus calibrates its coulomb counter against the cell's discharge curve. Running fast charge into an uncalibrated cell pushes current before the IC has set its baseline — you get inaccurate percentage readings from the first charge onward.
Sudden shutdown at 20–30% on a freshly installed BM37
This is a voltage cliff problem, not a capacity problem. Under modem load or peak screen brightness, the new cell's internal resistance causes a voltage drop the phone's protection circuit reads as critically low — even though the fuel gauge still shows 20–30%. The BMS trips the cutoff before the gauge catches up. One full discharge-charge cycle without fast charging lets the coulomb counter recalibrate the discharge curve and push the cliff back to where it belongs — typically below 5%.
Phone reporting wrong battery percentage after cell replacement
The fuel gauge IC in the Mi 5s Plus stores a learned discharge curve from the old cell. Swapping the BM37 doesn't reset that curve automatically. The IC maps the new cell's voltage onto the old cell's profile, which shifts the percentage readout — sometimes by 10–15%. To reset it, drain the phone until it shuts off on its own, then charge uninterrupted to 100% with fast charging off. After one complete cycle, the coulomb counter rewrites the curve to the new cell and percentage reporting stabilises.