HTC BA S850 Desire C Replacement Battery 3.7V 1100mAh

HTC Desire C / A320E — 3.7V Li-ion Replacement Battery (BA S850)

This is a 3.7V, 1100mAh Li-ion cell replacing part number BA S850 in the HTC Desire C, Golf, A320E, and Desire 200. It fits the original battery bay with no modification. Voltage and capacity match the factory spec exactly.

• Desire C / Golf / A320E cross-compatibility: These models share the same battery bay dimensions, 3.7V nominal rail, and connector pinout. The BMS communicates over the same two data lines, so the fuel gauge IC accepts this cell without a firmware conflict.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a Desire C unit. The BMS accepted the cell on first insertion, charge current ramped correctly to CV phase, and no thermal events occurred at the charge IC.
• Fuel gauge recalibration on first use: On first installation, run one full discharge down to automatic shutdown, then charge uninterrupted to 100% before using the device again. This gives the coulomb counter a clean reference curve for the new cell and prevents erratic percentage readings from the first day.

Sudden shutdown at 20–30% on the Desire C after a cell swap

The Desire C uses a fuel gauge IC that tracks capacity against a stored discharge curve from the previous cell. When a new cell goes in, that curve no longer matches the actual voltage-versus-capacity relationship of the replacement. At around 3.6–3.7V under screen or modem load, the cell voltage dips briefly below the threshold the IC expects at 20–30%, triggering an emergency shutdown before the gauge catches up. One complete discharge-charge cycle overwrites the reference and the shutdowns stop.

Phone not powering on after the replacement battery sat in storage

Li-ion cells in storage self-discharge over time. If the cell drops below approximately 2.5V, the BMS enters a lockout state and blocks normal charge current to prevent damage to the depleted cell. The Desire C will show no boot screen and no charge indicator. Connect the phone to a wall adapter — not a PC USB port — and leave it for 20–30 minutes without pressing the power button. The charge IC trickle-charges the cell back above the BMS release threshold, typically around 2.9V, at which point normal charging resumes.