Cingular Flip 2 Replacement Battery 3.7V 1200mAh Li-ion

Cingular Flip 2 / QuickFlip / OT-4044C — 3.7V Li-ion 1200mAh Replacement Battery

This 3.7V Li-ion cell replaces the original battery in the Cingular Flip 2, QuickFlip, and OT-4044C clamshell phones. Capacity is 1200mAh (4.44Wh), matching the stock specification. If your phone shuts down unexpectedly, won't hold a charge, or no longer powers on, this cell addresses those failure points.

• Flip 2, QuickFlip, and OT-4044C compatibility: These three models share the same battery bay dimensions, connector pinout, and 3.7V voltage rail. The cell physically seats and makes contact the same way across all three variants.
• Bench tested on actual hardware: We cycled this cell through charge and load testing, confirming the BMS accepts the charge IC handshake and holds voltage within spec under simulated screen and modem draw without tripping the protection circuit.
• Fuel gauge recalibration on first cycle: After fitting this cell, run one full discharge down to automatic shutdown, then charge uninterrupted to 100% before normal use. The phone's fuel gauge IC was calibrated against the old cell's discharge curve — one complete cycle resets the coulomb counter baseline to the new cell.

Sudden shutdown at 20–30% on the Flip 2 after a cell swap

This is a voltage cliff problem, not a capacity problem. When the modem transmits or the backlight fires at full brightness, current draw spikes sharply. A new cell with an uncalibrated fuel gauge IC can report 25% remaining while actual cell voltage has already dropped below the BMS cutoff threshold under that load. The phone interprets this as a fault and shuts off. One full discharge-recharge cycle lets the coulomb counter map the new cell's actual voltage curve, and the shutdowns stop.

OT-4044C won't power on after sitting in storage

Li-ion cells left discharged in storage self-discharge slowly past the BMS lockout threshold — typically below 2.5V per cell. When voltage drops that low, the protection circuit opens and blocks all current flow, including from the charger. Plug the phone into a wall charger, not a USB port, and leave it connected for at least 30 minutes without pressing the power button. Wall chargers deliver enough trickle current to nudge the cell above the 2.8V recovery threshold and prompt the BMS to re-initialise.