Samsung SCH-i839 Replacement Battery 3.7V 850mAh Li-ion

Samsung SCH-i839 — 3.7V Li-ion Replacement Battery

This is a 3.7V 850mAh Li-ion replacement battery for the Samsung SCH-i839. It fits the SCH-i839 directly and restores power to calling, messaging, and standard phone functions. Capacity is 850mAh (3.15Wh), matching the original cell specification.

• SCH-i839 fit: The SCH-i839 uses a 3.7V single-cell Li-ion pack with a three-contact connector. This replacement matches that connector pinout and voltage rail, so the phone's charge IC and BMS handshake correctly without error flags.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the SCH-i839 platform. The BMS accepted the charge IC handshake on the first cycle, and the protection circuit tripped correctly at the low-voltage cutoff threshold — no false trips under normal phone load.
• Fuel gauge recalibration on first install: On first use after installing this cell, disable fast charging if available and run one full discharge-to-charge cycle before resuming normal use. The fuel gauge IC on the SCH-i839 is calibrated to the old cell's discharge curve — a full cycle lets it recalibrate against the new cell before reporting accurate percentages.

Sudden shutdown at 20–30% on the SCH-i839 after a cell swap

This happens because the fuel gauge IC is still running the discharge curve it learned from the old, degraded cell. When the new cell hits a voltage point the IC hasn't mapped yet, it misreads remaining capacity. Under modem or screen load, the voltage drops briefly below the BMS cutoff threshold — and the phone shuts down even though the displayed percentage reads higher. One complete discharge cycle from 100% to auto-shutoff, followed by a full charge, resets the coulomb counter and corrects the curve. After that cycle, shutdowns at false-high percentages stop.

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

Li-ion cells stored fully discharged can drop below 2.5V per cell, which triggers a BMS lockout to prevent damage. The SCH-i839 will show no sign of life — no boot screen, no charge indicator — when this happens. Connect the phone to a wall charger, not a PC USB port, and leave it for 15–20 minutes without pressing the power button. Most BMS circuits on this platform include a trickle-recovery path at around 2.8V that will wake the cell enough to begin normal charging; once the charge LED activates, the battery is recovering.