AT&T Flip IV Compatible Battery 3.7V 1300mAh LT14H504357W

AT&T Flip IV / U102AA — 3.7V Li-ion Replacement Battery (LT14H504357W)

This is a 3.7V, 1300mAh Li-ion battery for the AT&T Flip IV (U102AA) flip phone. It replaces OEM part numbers LT14H504357W and TL14H504357W. The cell fits the Flip IV's internal bay and connects to the phone's charge IC and fuel gauge circuit directly.

• Flip IV and U102AA compatibility: Both model designations refer to the same hardware platform. They share the same connector pinout, voltage rail at 3.7V nominal, and BMS handshake with the phone's charge controller — one cell covers both.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Flip IV platform. The BMS accepted the cell without error, charge termination triggered correctly at 4.2V, and low-voltage cutoff engaged at the expected threshold.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging if available and run one full discharge-to-charge cycle. This lets the phone's fuel gauge IC recalibrate its coulomb counter against the new cell's discharge curve before drawing higher charge current into an uncalibrated cell.

Why the Flip IV reports wrong battery percentage after a cell swap

The Flip IV tracks charge state using a fuel gauge IC that builds a model of the cell's discharge curve over time. When you fit a new cell, that model still reflects the old, degraded cell. The gauge will read high early in discharge and drop sharply as the curve diverges from its stored data. One full discharge cycle — draining to auto-shutoff and charging back to 100% — forces the IC to rewrite its reference curve against the new cell. After that cycle, percentage readings stabilise.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops below the modem's minimum operating threshold under load, even though the gauge still shows charge remaining. The Flip IV's modem and screen draw a combined current spike that the fuel gauge IC, still running an old curve, fails to predict. The phone cuts out because actual cell voltage collapses below roughly 3.2V under that load. Run one full calibration cycle to align the gauge with the new cell — shutdowns at false percentages stop once the curve is accurate.