BTR5600B Cingular 2100 Replacement Battery 3.7V 2200mAh

Cingular 2100 / 2120 — 3.7V Li-ion Replacement Battery (BTR5600B)

This is a 3.7V Li-ion cell rated at 2200mAh (8.14Wh), built to the BTR5600B spec. It fits the Cingular 2100 and 2120 smartphones. Both models share the same battery bay geometry, connector pinout, and BMS handshake protocol.

• 2100 and 2120 compatibility: Both devices run off the same 3.7V single-cell architecture with identical connector orientation and BMS communication lines. The fuel gauge IC on each model reads cell impedance from the same data pin, so one cell revision covers both without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a 2100 unit. The BMS accepted the cell without fault codes, charge current ramped normally through CC-CV stages, and the protection circuit triggered correctly at the low-voltage cutoff threshold.
• Fuel gauge recalibration on first use: On first installation, run one full discharge to auto-off and one uninterrupted charge to 100% before using the device normally. The Cingular 2100's coulomb counter is calibrated to the original cell's discharge curve — a full cycle lets it remap against the new cell and report accurate percentages.

Sudden shutdown at 20–30% on the Cingular 2100

This is a voltage cliff issue, not a capacity defect. When an aged or deeply cycled cell can no longer hold voltage under the combined load of the modem radio and screen backlight, the cell voltage drops below the BMS cutoff threshold in milliseconds — faster than the OS can log it. The phone reads 25% one second and shuts off the next. Replacing the cell resolves this because a fresh cell sustains voltage above 3.4V under that same load. After fitting the new cell, confirm normal operation by checking that the phone holds a stable percentage reading under a voice call or hotspot session.

Phone not powering on after the battery sat in storage

Li-ion cells that discharge below approximately 2.5V per cell trigger a BMS lockout — the protection circuit opens and blocks current flow entirely to prevent damage. The phone will show nothing when you press the power button, and a standard wall charger may not deliver enough initial current to wake a locked-out BMS. Connect the phone to a USB port on a powered laptop rather than a wall adapter, which tends to trickle a lower initial current that some BMS circuits respond to for re-initialisation. Once the percentage appears on screen — even at 1% — switch to a wall charger and complete a full charge cycle before use.