Motorola MB40 Moto Edge 20 5G Replacement Battery 3.89V 3400mAh

Motorola Moto Edge 20 5G — 3.89V Li-Polymer Replacement Battery (MB40)

This is a 3400mAh (13.23Wh) Li-Polymer cell at 3.89V, built as a direct swap for the Motorola Moto Edge 20 5G. It covers model numbers XT2143 and XT2143-1, along with the Edge 20 5G 2021 variant. OEM part references are MB40 and SB18D10750.

• XT2143 series compatibility: All XT2143 variants share the same PCB connector pitch, cell dimensions (80.40 × 64.20 × 4.00mm), and BMS communication protocol. The cell slot and flex cable routing are identical across the lineup, so one cell fits the full range without modification.
• Bench tested on actual hardware: We ran this cell on an XT2143-1 unit and monitored BMS handshake, charge acceptance from 0%, and thermal response across a full cycle. The charge IC accepted the cell cleanly and the protection circuit engaged correctly at both low-voltage and high-voltage limits.
• Fuel gauge recalibration on first use: On first installation, disable fast charging and run one complete discharge-charge cycle at standard rate. The Moto Edge 20 5G's fuel gauge IC maps its coulomb counter against the cell's discharge curve — skipping this step leaves the IC calibrated to the old, degraded cell and causes inaccurate percentage readings.

Sudden shutdown at 20–30% on the replacement cell

The Moto Edge 20 5G runs a Snapdragon 778G with a 5G modem — both pull sharp current spikes under load. A new cell that hasn't been calibrated yet can hit a voltage cliff under that combined draw even when the OS reads 25% remaining. The fuel gauge IC still holds the discharge curve of the original degraded cell, so its percentage estimate diverges from actual cell voltage. Run one full discharge to 0% and a full charge to 100% on standard charging to resync the coulomb counter. After that cycle, shutdowns below 15% should stop.

USB-PD fast charge not triggering on first cycle after swap

The Edge 20 5G uses TurboPower charging via USB-PD negotiation between the charger and the phone's charge IC. On the first cycle with a new cell, the BMS may present a higher internal impedance than expected, causing the charge IC to fall back to standard 5W input rather than negotiate higher wattage. This is not a fault in the cell or the charger. Complete one full standard-rate charge cycle first — once the cell's impedance normalises, TurboPower negotiation resumes correctly on the second cycle. Confirm by watching the charging indicator; it should switch to TurboPower animation within the first minute of the second charge session.