Navon Mizu BT70 3.7V Replacement Battery 1200mAh Li-ion

Navon Mizu BT-70 — 3.7V Li-ion Replacement Battery (BT70)

This 3.7V, 1200mAh Li-ion cell is a direct replacement for the Navon Mizu BT-70 and Mizu BT70 smartphones. It slots into the original battery bay and connects to the same three-contact board the phone's charge IC expects. Capacity is 1200mAh (4.44Wh), matching the factory specification.

• Mizu BT-70 and BT70 fit: Both model designations use the same physical cell format, connector pitch, and BMS handshake. One cell covers both variants without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a bench rig, confirmed the BMS accepted the charge IC handshake correctly, and verified cell voltage held stable under a simulated screen-plus-modem load.
• Fuel gauge recalibration on first use: After installation, disable fast charging and run one full discharge-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell — skipping this step causes erratic percentage readings.

Why the Mizu BT-70 reports wrong battery percentage after a cell swap

The Mizu BT-70 uses a fuel gauge IC that learns the battery's discharge curve over cycles. When a new cell goes in, the IC still holds the old cell's calibration data. The percentage shown on screen is calculated against a curve that no longer matches the physical cell. One full discharge to automatic shutdown followed by a full charge at standard rate resets this — after that cycle, percentage accuracy returns to normal.

Sudden shutdown at 20–30% remaining on the Mizu BT-70

This happens when the cell voltage drops below the BMS cutoff threshold under the combined load of the modem radio and display — even though the fuel gauge still shows charge remaining. Older or deeply discharged cells hit this voltage cliff faster. On a new replacement cell, this symptom typically appears if the fuel gauge IC hasn't yet recalibrated. Run one full cycle at standard charge rate; if shutdown still occurs below 3.5V under load, the BMS cutoff voltage is doing its job and the cell is within normal parameters.