Virgin Mobile Montage SPH-M350 Replacement Battery 3.7V 940mAh 0.1 lb

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

This is a 3.7V, 940mAh Li-ion battery for the Virgin Mobile Montage (SPH-M350). It replaces a degraded or failed original cell and restores full function to calling, texting, and standby operation. Dimensions are 54.72 × 41.58 × 4.12mm — confirm your original cell matches before installing.

• Montage / SPH-M350 fit: Both model names refer to the same handset sold under different identifiers. The battery connector, voltage rail, and physical footprint are identical across both SKUs, so one cell covers either label.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the SPH-M350 platform. The BMS accepted the charge handshake without fault flags, and voltage held stable under combined screen and radio load.
• Fuel gauge recalibration on first use: After installing this cell, run one complete discharge down to automatic shutoff, then charge uninterrupted to 100% before normal use. The Montage's fuel gauge IC recalibrates its coulomb counter against the new cell's discharge curve during this first cycle.

Sudden shutdown at 20–30% on the Montage after a cell swap

This is a voltage cliff failure, not a capacity issue. When the modem transmits or the screen peaks in brightness, current draw spikes sharply. A new cell that hasn't been calibrated can't sustain voltage under that load, and the BMS cuts power to protect the cell before the percentage display reaches zero. One full discharge-charge cycle lets the fuel gauge IC map the actual voltage-to-capacity curve of the new cell. After calibration, the shutoffs stop because the system accurately predicts the low-voltage threshold before it's hit.

Phone won't power on after the replacement battery sat in storage

Li-ion cells self-discharge in storage. If the cell voltage dropped below approximately 2.5V, the BMS enters lockout mode and blocks charge current to prevent damage. The phone won't respond to the power button and may show nothing on the charger. Connect to a wall charger — not USB from a PC — and leave it for 20–30 minutes without pressing anything. Most BMS circuits begin a trickle pre-charge recovery at around 2.5V and will re-initialise; the charging indicator should appear before the 30-minute mark.