HTC Ace Replacement Battery BA S470 3.7V 1050mAh

HTC Desire HD / Ace — 3.7V Li-ion Replacement Battery (BA S470)

This is a 3.7V, 1050mAh Li-ion replacement battery for the HTC Ace and Desire HD family of Android smartphones. It also fits the A9191 and Surround variants that share the same battery bay and connector. Capacity is 1050mAh (3.89Wh), matching original spec.

• Ace and Desire HD platform compatibility: These models share the same physical footprint, connector pinout, and BMS handshake protocol — the BA S470 part number covers the full range without modification.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Desire HD unit. The BMS accepted charge from a stock HTC charger without fault codes, and protection circuitry tripped correctly at low-voltage cutoff.
• Fuel gauge recalibration on first use: On first installation, run one complete discharge to automatic shutdown, then charge uninterrupted to 100% before use. This gives the phone's fuel gauge IC a full reference curve against the new cell — skipping this step causes erratic percentage readings for the first several cycles.

Why the Desire HD reports wrong battery percentage after a cell swap

The Desire HD uses a coulomb counter and learned discharge curve stored against the old cell. When a new cell goes in, that stored curve no longer matches the actual voltage-to-capacity relationship of the replacement. The phone reads voltage, maps it to the old curve, and outputs an inaccurate percentage. One full discharge-to-shutdown followed by an uninterrupted charge forces the fuel gauge IC to relearn the curve against the new cell's chemistry. After that cycle, percentage accuracy returns to normal.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff, not a capacity fault. Under modem radio or display load, the cell voltage drops sharply below the threshold the BMS will sustain — even if the fuel gauge still shows charge remaining. It happens most often when the fuel gauge IC hasn't completed recalibration. Run one full discharge cycle and let the phone shut off on its own. If shutdowns persist past two full cycles, check that resting voltage sits above 3.6V after a full charge using a multimeter on the battery terminals.