Sagem MYC-3 287024051 Replacement Battery 3.7V 900mAh

Sagem MYC-3 Series — 3.7V Li-ion Replacement Battery (287024051)

This is a 3.7V 900mAh Li-ion cell for the Sagem MYC-3 family of compact GSM candybar phones. It fits the MYC-3, MYC-3b, MYC3-2, and MYC32. Capacity matches the original OEM specification at 3.33Wh.

• MYC-3 family compatibility: The MYC-3, MYC-3b, MYC3-2, and MYC32 share the same battery bay dimensions, connector pinout, and 3.7V nominal voltage rail. One cell fits all four variants without modification.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the MYC-3 platform. The BMS held charge cutoff at 4.2V and low-voltage cutoff engaged correctly before cell damage threshold.
• Fuel gauge recalibration on first use: On first installation, disable any fast-charge adapter and run one complete discharge-to-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve before accepting higher charge current into an uncalibrated cell.

Why the MYC-3 reports wrong battery percentage after a cell swap

The MYC-3 uses a fuel gauge IC that stores a charge curve calibrated to the original cell. When you fit a new cell, that stored curve no longer matches actual cell behaviour. The IC reads voltage and estimates state-of-charge against outdated data, so the percentage shown on screen drifts from reality. One full discharge down to auto-shutoff followed by a complete charge resets the reference points the IC uses for calculation.

Sudden shutdown at 20–30% on the replacement cell

This happens when the GSM modem fires a high-current transmit burst and cell voltage collapses faster than the fuel gauge IC expects. The phone's protection circuit reads the voltage drop as a critical low and cuts power immediately. It is a calibration gap, not a faulty cell. Run two full discharge-charge cycles and confirm the cell stays above 3.6V under screen-on load before flagging a fault.