Sigmatel FXD 6100 Replacement Battery 3.7V 1050mAh

Sigmatel FXD 6100 — 3.7V Li-ion Replacement Battery

This is a 3.7V, 1050mAh Li-ion replacement battery for the Sigmatel FXD 6100 smartphone. It fits directly into the FXD 6100 and restores full power to a device suffering from a degraded or failed original cell. Capacity is 1050mAh (3.89Wh) as specified for this model.

• FXD 6100 fit: This battery matches the voltage rail and physical dimensions (53.00 × 33.90 × 5.60mm) of the original FXD 6100 cell. The connector and BMS interface align with what the phone's charge IC expects, so the device recognises the new cell on first boot.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS held stable cutoff thresholds at both ends, with no false tripping under simulated screen and modem load.
• First-cycle fuel gauge recalibration: On first use after installation, disable fast charging if the option is available and run one complete discharge-charge cycle. The FXD 6100's fuel gauge IC is calibrated to the old cell's discharge curve — one full cycle lets it map the new cell's behaviour before resuming high-current charging.

Why the FXD 6100 reports wrong battery percentage after a cell swap

The FXD 6100 uses a fuel gauge IC that tracks charge state using a coulomb counter trained on the original cell's discharge curve. When you swap in a new cell, the counter starts from stale reference data. This causes the OS to display percentages that don't reflect actual charge state — you may see jumps of 10–15% in either direction. One full discharge down to automatic shutdown, followed by a complete charge to 100%, resets the counter against the new cell's actual curve.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC still holds the old cell's voltage-versus-capacity mapping. The new cell hits a steeper voltage cliff under modem or display load — the phone's hardware protection circuit cuts power before the reported percentage reaches zero. It's not a faulty battery. Force a full discharge cycle: let the phone shut itself off naturally, then charge uninterrupted to 4.2V (100%). After one cycle, the shutdown point shifts back to the correct low-voltage threshold.