About this replacement
Xiaomi Mi Max / Mi Max Dual SIM — 3.85V Li-Polymer Replacement Battery (BM49)
This is a 3.85V, 4750mAh (18.29Wh) Li-Polymer cell built to replace the BM49 battery in the Xiaomi Mi Max and Mi Max Dual SIM. It fits the standard 2016001 chassis and the TD-LTE 16GB variant. The physical dimensions are 99.50 × 76.40 × 3.40mm — measure your original before fitting if you are unsure of your exact variant.
- Mi Max platform compatibility: The Mi Max and Mi Max Dual SIM variants all share the same battery bay geometry, BM49 part number, and 3.85V nominal voltage rail. The BMS connector pinout is identical across these variants, so one cell covers the full range listed.
- Bench tested on actual hardware: We ran this cell on a Mi Max unit and cycled it through a full charge sequence. The BMS accepted charge without fault flags, and the charge IC stepped down from CC to CV at the correct voltage ceiling with no thermal events.
- Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging for one complete discharge-to-charge cycle. The Mi Max fuel gauge IC recalibrates its coulomb counter against the new cell's discharge curve. Running fast charge before that cycle completes can push high current into an uncalibrated cell and skew percentage readings for weeks.
Sudden shutdown at 20–30% on the Mi Max after a cell swap
The Mi Max shuts down mid-use despite showing charge remaining because the fuel gauge IC is still calibrated to the old cell's discharge curve. A new cell has a slightly different voltage-to-capacity curve, so the gauge miscalculates the voltage cliff. Under high screen or modem load, the cell voltage drops faster than the gauge predicts, triggering an emergency shutdown. Run two full discharge-and-charge cycles without fast charging — by the end of the second cycle, the coulomb counter has enough data to track the new cell accurately.
Mi Max not powering on after the battery sat discharged in storage
If a BM49 cell drops below approximately 2.5V during storage, the BMS enters a lockout state and will not pass current to the device. The phone shows nothing — no charge animation, no boot. Connect the device to a wall charger rated at 5V/1A or higher and leave it for 20–30 minutes before attempting to power on. The charge IC applies a trickle pre-charge to bring the cell back above the BMS re-enable threshold, typically around 3.0V, before normal charging resumes.