Virgin Mobile Montage 3.7V Compatible Battery 900mAh

Virgin Mobile Montage / SPH-M350 — 3.7V Li-ion Replacement Battery

This is a 3.7V, 900mAh Li-ion battery for the Virgin Mobile Montage (SPH-M350) smartphone. It fits the battery bay directly and connects to the phone's charge and fuel gauge circuits. Capacity is 900mAh (3.33Wh), matching the original cell specification.

• Montage / SPH-M350 fitment: Both model names refer to the same handset sold across different retail channels. The battery bay dimensions, connector pinout, and BMS communication protocol are identical across both variants — one cell fits both.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the SPH-M350 platform. The BMS accepted the cell without error flags, and the charge IC negotiated current correctly from the first cycle.
• Fuel gauge recalibration on first use: On first installation, run one complete discharge-charge cycle with fast charging disabled. The SPH-M350 fuel gauge IC holds calibration data from the old cell — one full cycle against the new discharge curve resets it and stops erratic percentage readings.

Why the Montage reports wrong battery percentage after a cell swap

The SPH-M350 uses a coulomb counter in the fuel gauge IC that builds its model against the old cell's discharge curve. When you install a fresh cell, that model is stale. The phone reads voltage and maps it against the old curve, so the percentage shown can be off by 15–25% until the IC relearns. One full discharge to auto-shutoff followed by a complete charge cycle forces the IC to recalibrate against the new cell. After that cycle, percentage accuracy returns to normal.

Sudden shutdown at 20–30% on the replacement cell

This happens when the phone's load — modem transmit bursts or screen brightness spikes — pulls more current than the cell voltage can sustain. The cell voltage drops below the BMS cutoff threshold even though the fuel gauge still shows charge remaining. It is a voltage cliff, not a capacity problem. The fix is to let the fuel gauge IC complete one full calibration cycle as above — once the IC has an accurate model of the new cell, it adjusts the low-voltage warning point and the early shutdowns stop.