Samsung EB494865VO Replacement Battery 3.7V 1900mAh

Samsung SPH-M840 / Galaxy Prevail II — 3.7V Li-ion Replacement Battery (EB494865VO)

This is a 3.7V, 1900mAh Li-ion cell built to the EB494865VO specification. It fits the Samsung SPH-M840 (Exhibit 4G), Galaxy Prevail II, and Galaxy Prevail 2. Voltage and capacity match the original factory spec exactly.

• SPH-M840 and Prevail II platform fit: These models share the same battery bay geometry, connector pinout, and BMS handshake. The 3.7V nominal rail feeds the same PMIC across all listed variants, so one cell covers the entire group.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the SPH-M840. The BMS accepted the cell without error flags, and the charge IC stepped through trickle, constant-current, and constant-voltage phases as expected.
• Fuel gauge recalibration on first use: After installing this cell, disable fast charging and run one full discharge-to-charge cycle before normal use. The phone's fuel gauge IC was calibrated against the old cell's discharge curve — one complete cycle lets it remap to the new cell and report accurate percentages.

Sudden shutdown at 20–30% on the SPH-M840 after a cell swap

This happens because the fuel gauge IC still holds the degraded discharge curve from the original cell. When the modem transmits or the screen ramps brightness, current draw spikes. The new cell's actual voltage under that load drops faster than the IC expects, so it triggers an emergency shutdown well before the displayed percentage hits zero. The fix is one full discharge cycle — drain to automatic power-off, then charge uninterrupted to 100% — so the coulomb counter resets against the new cell's actual curve. After that cycle, shutdown-at-30% behaviour stops.

Phone not powering on after the replacement battery sat in storage

Li-ion cells self-discharge in storage. If this cell sat long enough to drop below 2.5V, the BMS enters lockout mode and blocks current flow to protect the cell from damage. The phone shows nothing — no boot logo, no charging indicator. Connect the phone to a wall charger, not a PC port, and leave it for 20–30 minutes without pressing the power button. The charge IC delivers a low-current trickle that slowly brings the cell voltage back above the BMS recovery threshold, typically around 2.9–3.0V, at which point normal charging resumes.