Samsung SCH-S800 Replacement Battery 3.7V 1150mAh Li-ion

Samsung SCH-S800 Series — 3.7V Li-ion Replacement Battery

This is a 3.7V, 1150mAh Li-ion replacement battery for the Samsung SCH-S800, SCH-S811, SCH-S810, and SCH-S850. These are early-to-mid 2000s Samsung mobile phones that share the same battery bay and cell specification. The original cells in phones this age are well past their cycle life — this replacement restores the phone to working condition.

• SCH-S800 series compatibility: The S800, S811, S810, and S850 share the same 3.7V single-cell configuration and connector pinout. The BMS on each device reads cell voltage from the same contact points, so one cell spec covers the full group without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the SCH-S800 platform. The BMS accepted the cell at first connection, charged to 4.2V cutoff without error, and discharged cleanly to the low-voltage protection threshold.
• Fuel gauge recalibration after installation: On first install, run one full uninterrupted discharge down to automatic shutoff, then charge to 100% without interruption. This lets the fuel gauge IC map the new cell's discharge curve before it begins reporting percentage to the OS.

Why the SCH-S800 reports wrong battery percentage after a cell swap

The fuel gauge IC on these Samsung phones stores a learned discharge curve from the previous cell. When you install a new cell, the IC still references the old curve, so the percentage readout drifts — often reading 40% when the cell is nearly flat. One full discharge-charge cycle forces the IC to relearn the curve against the new cell's actual voltage profile. After that cycle, percentage accuracy returns to normal.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff — not a capacity problem. When the phone draws peak current for a call or backlight burst, the cell voltage drops sharply under load. If the IC hasn't calibrated to the new cell yet, it triggers low-voltage protection at a higher state of charge than necessary. Run one full discharge cycle first. If the shutdowns continue after calibration, check that the battery contacts on the phone are clean and making firm contact — dirty contacts add resistance that worsens voltage sag under load.