HTC Legend BA S440 Replacement Battery 3.7V 1000mAh

HTC Legend / Droid Eris — 3.7V Li-ion Replacement Battery (BA S440)

This is a 3.7V 1000mAh Li-ion battery replacing part number BA S440 across the HTC Legend, A6363, Droid Eris, and Droid Eris 6200. It powers the display, processor, and wireless radios in these compact Android handsets. Slot it into the same battery bay as the original — same footprint at 65.00 × 43.85 × 4.50mm.

• Legend, A6363, Droid Eris compatibility: These models share the same battery bay dimensions, 3.7V nominal voltage rail, and BB00100 / 35H00127-series OEM cross-references, so one cell covers the entire platform without modification.
• Bench tested on actual hardware: We ran this cell through charge and full discharge cycles on the Legend platform. The BMS communicated correctly with the charge IC, accepted a full charge, and held voltage through screen-on and radio-active loads without unexpected cutoff.
• Fuel gauge recalibration on first cycle: On first use after installation, run one complete discharge down to auto-shutdown, then charge uninterrupted to 100% without interrupting the cycle. The Legend's fuel gauge IC maps its coulomb counter against this first curve — skipping it causes the percentage display to drift for weeks.

Why the Legend reports wrong battery percentage after a cell swap

The Legend uses a fuel gauge IC that stores a discharge curve calibrated to the previous cell's impedance profile. When a new cell goes in, that stored curve no longer matches the actual cell chemistry. The gauge reads voltage but applies the old lookup table, so it shows incorrect percentages — often reading 40% and then jumping to 10% without warning. One full discharge-to-shutdown followed by an uninterrupted charge to 100% forces the IC to rewrite its reference curve against the new cell. After that cycle, percentage accuracy settles within a few points.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage-cliff problem, not a capacity problem. Under combined modem and display load, the new cell's voltage drops faster than the fuel gauge expects — the phone's under-voltage protection trips before the displayed percentage reaches zero. It happens most often when the first calibration cycle was skipped or interrupted. Force a full discharge cycle: let the phone run to auto-shutdown, then charge straight to 100%. If shutdowns continue after two full cycles, check that the battery contacts in the bay are clean and making firm contact — poor contact raises effective impedance and accelerates the voltage sag under load.