About this replacement
Navon Mizu M402 / D402 — 3.7V Li-ion Replacement Battery (G64495)
This is a 3.7V, 1400mAh Li-ion cell for the Navon Mizu M402 and Mizu D402 smartphones. It replaces OEM part number G64495 directly. Fit the new cell when the original no longer holds a useful charge or fails to power the device.
- Mizu M402 and D402 compatibility: Both models share the same battery bay dimensions and connector pinout. The 56.30 × 51.90 × 4.60mm cell fits either device without modification. Voltage rail and connector orientation are identical across the two.
- Bench tested on actual hardware: We cycled this cell through a full discharge and charge sequence on a Navon platform. The BMS accepted the cell without lockout, and charge termination triggered correctly at 4.2V. No thermal events or charge IC faults were recorded.
- Fuel gauge recalibration on first use: After fitting this cell, disable fast charging for the first complete discharge-charge cycle. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging begins. Skipping this step is the main reason percentage readings drift in the first week.
Why the Mizu M402 reports wrong battery percentage after a cell swap
The Mizu M402 uses a fuel gauge IC that tracks battery state based on a learned discharge curve from the original cell. When a new cell goes in, the IC still references the old curve — so the percentage shown on screen does not match actual charge. One complete slow discharge down to automatic shutdown followed by a full charge corrects this. After that cycle, the IC recalibrates its coulomb counter against the new cell and percentage readings stabilise.
Sudden shutdown at 20–30% on the replacement cell
This happens because the cell voltage drops sharply under load — modem transmission bursts and screen brightness spikes pull more current than the fuel gauge IC expects at that state of charge. The phone shuts down before the displayed percentage reaches zero. It is a voltage sag issue, not a faulty cell. Run two full slow cycles first — this trains the fuel gauge IC to cut off display percentage closer to the real voltage cliff, typically around 3.5V under load.