AT&T One X Plus Replacement Battery 3.8V 2000mAh

AT&T One X Plus / S728e — 3.8V Li-Polymer Replacement Battery

This 3.8V, 2000mAh Li-Polymer battery is a direct cell replacement for the AT&T HTC One X Plus (S728e). It fits the original battery cavity and connects to the device's charge IC and fuel gauge circuit. Capacity is 2000mAh (7.6Wh) — matching the stock specification.

• One X Plus and S728e compatibility: Both model designations share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The 60.50 × 54.00 × 4.80 mm cell fits without modification to either variant.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the One X Plus platform. The BMS accepted the cell without fault flags, and the charge IC transitioned correctly from constant-current to constant-voltage phase at the expected 4.35V ceiling.
• Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging for one complete discharge-to-charge cycle. The fuel gauge IC is calibrated to the old cell's discharge curve. Running one slow cycle first lets the coulomb counter build an accurate model before high-current charging begins.

Why the One X Plus reports wrong battery percentage after a cell swap

The One X Plus uses a coulomb-counting fuel gauge IC that tracks charge state against a stored discharge curve from the original cell. When you install a new cell, that stored curve no longer matches the actual voltage-to-capacity relationship. The gauge reads voltage correctly but maps it to the wrong percentage. One full slow discharge followed by a full charge resets the reference and restores accurate reporting.

Sudden shutdown at 20–30% on the replacement cell

This happens when the modem radio or display draws a current spike the cell cannot sustain at low state-of-charge. Voltage drops sharply — briefly falling below the BMS undervoltage threshold — and the device shuts down even though the gauge still shows charge remaining. It is a voltage-sag failure, not a capacity failure. After the fuel gauge IC completes one full recalibration cycle, the shutdown threshold and reported percentage align more accurately, and the abrupt cutoff typically resolves. If it persists past two full cycles, check that the cell connector is fully seated.