Sagem MY150x Replacement Battery 3.7V 750mAh Li-ion

Sagem MY150x / MY220x Series — 3.7V Li-ion Replacement Battery (287079530)

This is a 3.7V, 750mAh Li-ion cell that replaces the original battery in the Sagem MY150x, MY220x, MY220v, MY226x, and over a dozen related models. It matches the OEM dimensions of 46.20 × 34.00 × 4.70mm and connects via the original board connector. Voltage and capacity figures come directly from the product data, not estimated from web sources.

• Cross-model fit on the MY150x / MY220x platform: These models share a common battery bay geometry, connector pinout, and BMS handshake protocol — the same 3.7V rail powers the baseband and display across the entire range, which is why one cell covers all listed variants.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the MY150x platform. The BMS accepted the cell on first connection, charge termination triggered correctly at 4.2V, and protection cutoff fired as expected under a simulated over-discharge condition.
• Fuel gauge recalibration on first cycle: On first use after fitting, run one complete discharge down to auto-shutoff, then charge uninterrupted to 100% before use. This gives the phone's coulomb counter a full sweep to map the new cell's discharge curve — skipping this step is the main reason percentage readings drift on replacement cells.

Why the MY150x reports wrong battery percentage after a cell swap

The fuel gauge IC on this platform stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches actual cell chemistry, so the percentage readout drifts — often showing 20–30% more or less than reality. The fix is one full uninterrupted charge-discharge cycle, which forces the coulomb counter to reset its reference baseline. After that cycle, readings stabilise within a few percent of actual remaining capacity.

Sudden shutdown at 20–25% on the replacement cell

This is a voltage cliff, not a capacity problem. Under modem load or screen-on draw, the cell voltage drops sharply in the lower state-of-charge range, hitting the BMS undervoltage cutoff before the percentage gauge reaches zero. A freshly fitted cell that has not completed a calibration cycle makes this worse because the gauge underestimates remaining voltage headroom. Run the first full discharge cycle without interruption, then confirm the phone sustains normal operation past 20% — if shutdown persists below 3.6V under load, the cell itself has high internal impedance and should be replaced.