HTC Desire 20 Pro Q6655 Compatible Battery 3.85V 4800mAh

HTC Desire 20 Pro — 3.85V Li-Polymer Replacement Battery (Q6655)

This is a 3.85V, 4800mAh Li-Polymer replacement battery for the HTC Desire 20 Pro smartphone. Part number Q6655 matches the original cell format and connector used in this device. It restores power to the display, processor, cameras, and radio stack when the original cell can no longer hold adequate charge.

• Desire 20 Pro cell fitment: The Q6655 cell shares the same footprint (87.40 × 65.30 × 4.80mm), voltage rail, and flex connector as the factory unit. The BMS on this device negotiates charge current via the charge IC — the replacement cell must present the correct impedance profile at first contact or charging will stall at trickle rate.
• Bench tested on actual hardware: We ran this cell through a full charge-discharge cycle on the Desire 20 Pro platform. The BMS accepted the cell without error flags, charge IC ramped to normal current after the initial handshake, and the fuel gauge IC tracked state-of-charge without jumping during the first cycle.
• First-cycle fast charge protocol: On first use after installation, disable fast charging and complete one full discharge-charge cycle at standard rate. This lets the fuel gauge IC recalibrate its coulomb counter against the new cell's actual discharge curve before high-current charging is applied to an uncalibrated cell.

Why the Desire 20 Pro reports wrong battery percentage after a cell swap

The fuel gauge IC stores a learned discharge curve from the original cell. After a replacement, that stored curve no longer matches the new cell's chemistry profile, so the IC reports inaccurate state-of-charge readings. Percentage can read 30% and then jump to 10% within minutes under moderate load. One complete slow-rate discharge to automatic shutdown followed by a full charge resets the coulomb counter and aligns the IC to the new cell curve.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff issue, not a capacity fault. Under high-current load — modem transmitting, screen at full brightness, GPS active — the cell voltage drops faster than the fuel gauge IC predicts, falling below the BMS cutoff threshold before the reported percentage reaches zero. The fix is completing the first-cycle recalibration described above so the IC maps the new cell's actual voltage-to-capacity curve. After one full calibration cycle, shutdowns at 20–30% typically stop; if they persist, confirm resting cell voltage sits above 3.85V after a full charge.