AT&T Quickfire BTR75 Compatible Battery 3.7V 1100mAh

AT&T Quickfire / GTX75 — 3.7V Li-ion Replacement Battery (BTR75)

This is a 3.7V, 1100mAh Li-ion replacement for the original BTR75 battery. It fits the AT&T Quickfire and GTX75 smartphones. The cell matches the OEM voltage rail and connector footprint of both devices.

• Quickfire and GTX75 compatibility: Both models share the BTR75 battery format — same 3.7V nominal rail, same connector pinout, same physical envelope at 65.71 × 53.23 × 6.40mm. The BMS handshake is consistent across both, so no firmware mismatch occurs on power-on.
• Bench tested on actual hardware: We cycled the BTR75 replacement through charge and discharge on bench equipment. The BMS held the charge termination voltage correctly and the protection circuit tripped as expected at the low-voltage cutoff threshold.
• Fuel gauge recalibration on first use: After installing this cell, disable fast charging for the first full discharge-charge cycle. The Quickfire's fuel gauge IC is calibrated to the old cell's discharge curve — running one uninterrupted cycle at standard current lets the coulomb counter reset its reference before high-current charging begins.

Why the Quickfire reports wrong battery percentage after a cell swap

The Quickfire uses a fuel gauge IC that tracks charge state by counting current in and out of the cell — a process called coulomb counting. When you replace the cell, the IC still holds the discharge curve data from the old battery. Until it runs a full cycle against the new cell, the percentage reading drifts from the real state of charge. One complete discharge to 3.3V and a full charge back to 4.2V at standard current resets the reference. After that cycle, percentage accuracy stabilises.

Sudden shutdown at 20–30% on a freshly installed BTR75

This usually happens because the fuel gauge IC hasn't recalibrated yet — it estimates 20–30% remaining, but the actual cell voltage has already dropped below what the modem or screen load can sustain. The BMS cuts power when cell voltage sags below roughly 3.0V under that load, even though the percentage display hasn't caught up. Run one full uninterrupted discharge-charge cycle at standard current. After calibration, the IC maps the cutoff threshold to the correct displayed percentage.