Motorola Moto Z4 KZ40 Replacement Battery 3.85V 3350mAh

Motorola Moto Z4 / XT1980-3 — 3.85V Li-Polymer Replacement Battery (KZ40)

This is a 3350mAh Li-Polymer cell rated at 3.85V, replacing the OEM KZ40 battery in the Motorola Moto Z4 and XT1980-3 smartphones. It restores power capacity to phones where the original cell no longer holds a useful charge. Dimensions are 78.70 × 62.52 × 4.10mm — match these before ordering.

• Moto Z4 and XT1980-3 fit: Both variants use the same KZ40 cell form factor, voltage rail, and connector pinout. The BMS handshake is identical across the XT1980-3 hardware revision, so one cell covers both.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Moto Z4 unit. The BMS accepted the cell without error flags, and fast-charge negotiation completed normally after the first full cycle.
• Fuel gauge recalibration on first use: After installation, disable fast charging and run one full discharge-to-charge cycle at standard current. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging begins on an uncalibrated cell.

Sudden shutdown at 20–30% on the Moto Z4 after a cell swap

This happens because the fuel gauge IC is still calibrated to the old cell's voltage curve. A new cell has a steeper voltage cliff at the lower end — the phone reads 25% but the actual cell voltage drops below the modem's sustain threshold under load. The BMS triggers a protection cutoff before the OS can react. One full discharge cycle from 100% to automatic shutdown, then a full charge, resets the coulomb counter to the new cell's curve.

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

On the first charge after a cell swap, the charge IC may default to slow charge while it verifies the new cell's impedance. This is normal — the controller is running a trickle-phase check before enabling high-current input. Do not assume the battery is faulty. Complete one full standard-rate charge cycle, then reconnect the fast charger. Fast-charge negotiation typically resumes from the second cycle onward once the IC has confirmed cell integrity.