Xiaomi Mi 8 SE BM3D Replacement Battery 3.85V 3100mAh

Xiaomi Mi 8 SE — 3.85V Li-Polymer Replacement Battery (BM3D)

This is a 3.85V, 3100mAh (11.94Wh) Li-Polymer cell built to replace the BM3D battery in the Xiaomi Mi 8 SE. It fits the Mi 8 SE, Mi 8 SE Standard Dual SIM, Mi 8 SE Standard Dual SIM TD-LTE, and M1805E2A variants. Physical dimensions are 68.80 × 62.55 × 3.90mm — matching the original cell footprint inside the chassis.

• Mi 8 SE variant coverage: All listed variants — Standard, Dual SIM, TD-LTE, and M1805E2A — share the same BM3D cell format, connector pinout, and BMS handshake protocol. One cell fits all four without modification.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on Mi 8 SE hardware. The BMS accepted charging handshake correctly, cutoff triggered cleanly at the low-voltage threshold, and no thermal flags fired during charge.
• Fuel gauge recalibration on first use: Disable fast charging for the first complete discharge-charge cycle after installation. The Mi 8 SE's fuel gauge IC is calibrated to the old cell's discharge curve — one slow cycle lets it remap against the new cell before high-current charging begins.

Sudden shutdown at 20–30% on the BM3D replacement cell

This happens because the Mi 8 SE's fuel gauge IC still references the discharge curve from the degraded original cell. When the new cell hits a voltage point the IC wasn't expecting, MIUI interprets it as a critical low and forces shutdown — even though usable charge remains. The fix is one full uninterrupted discharge to automatic shutdown followed by a complete charge to 100% with fast charging off. After that cycle, the coulomb counter recalibrates and percentage readings stabilise. If shutdown still occurs early, check that the battery connector is fully seated — a partial connection raises internal resistance and causes premature voltage sag under modem load.

USB-PD fast charge not accepted on the first cycle after replacement

On the first charge cycle, the Mi 8 SE's charge IC may refuse Qualcomm Quick Charge negotiation with a new BM3D cell because the BMS presents a higher impedance than the IC expects from a known-good cell. The phone defaults to standard 5V charging as a safety fallback. Run that first cycle on a standard 5W charger — once the BMS logs an initial full cycle, the charge IC re-negotiates fast charge protocol on subsequent sessions. If fast charge still doesn't activate after the second cycle, verify the USB-C port is free of debris and the cable supports high-current delivery.