UMI UMIDIGI Z2 Pro Replacement Battery 3.85V 3350mAh

UMI UMIDIGI Z2 Pro — 3.85V Li-Polymer Replacement Battery (Z2 Pro)

This is a 3350mAh Li-Polymer cell at 3.85V nominal, built to replace the original battery in the UMIDIGI Z2 Pro smartphone. It restores power to the processor, display, camera, and all connectivity functions when the original cell has degraded or failed to hold a charge. Physical dimensions are 78.30 × 59.50 × 4.60mm — confirm against your existing cell before installation.

• UMIDIGI Z2 Pro fit: This cell matches the voltage rail and connector spec of the Z2 Pro. The BMS communicates with the phone's charge IC over the same pin configuration as the original, so the device recognises the cell and allows normal charge initiation.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the bench. The BMS held cutoff correctly at both ends — no false termination during charge, no undervoltage trip under simulated modem and display load.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one full discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes amperage into an uncalibrated counter — preventing erratic percentage readings early on.

Sudden shutdown at 20–30% on the replacement cell

A new cell can trigger abrupt shutdowns in the 20–30% range because the phone's fuel gauge IC is still calibrated to the old, degraded cell's discharge curve. When the modem fires for a call or data burst, current draw spikes and the new cell's voltage drops briefly below the shutdown threshold the IC has mapped. The phone interprets this as a dead battery and cuts power — even though the cell has remaining capacity. One complete discharge to 0% followed by a full uninterrupted charge resets the coulomb counter against the new cell's actual curve. After that cycle, shutdowns in this range stop.

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

Some Z2 Pro units will not negotiate fast charge on the first cycle with a new cell — the charge IC defaults to standard 5V/1A until the BMS has completed one handshake sequence. This is a protection behaviour, not a fault with the cell or charger. Plug into your fast charger after the first full standard charge cycle and the protocol negotiation completes normally. If fast charge still does not activate after two cycles, check the USB-C port for debris — a dirty contact disrupts the CC pin signal the PD controller needs to step up voltage.