HQRS 777 Smartphone Replacement Battery 3.7V 1200mAh

HQRS 777 — 3.7V Li-ion Replacement Battery

This is a 3.7V, 1200mAh (4.44Wh) Li-ion cell built to replace the original battery in the HQRS 777 smartphone. It targets devices where the stock cell has degraded, holds a short charge, or no longer powers on. Dimensions are 53.00 × 33.90 × 5.70mm — measure your original before installing.

• HQRS 777 fit: The 777 uses a fixed 3.7V single-cell architecture with a direct connector to the charge IC. This cell matches that voltage rail and connector pinout, so the charge IC can communicate with the BMS without a logic mismatch.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a 3.7V single-cell platform, monitoring BMS cutoff at both ends. The protection circuit tripped correctly at low voltage and the charge IC accepted the cell without fault codes.
• Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging begins on an uncalibrated reference.

Why the HQRS 777 reports wrong battery percentage after a cell swap

The fuel gauge IC on the 777 uses a coulomb counter calibrated to the original cell's discharge curve. When you install a new cell, that reference is stale. The IC doesn't know the new cell's actual capacity, so it reports percentages against the old curve. One full discharge-then-charge cycle forces the IC to relearn the endpoints and recalculate from a clean baseline.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops below what the modem or display load needs — typically under 3.5V — even though the gauge still reads 20–30%. It's a voltage cliff caused by the fuel gauge running on the wrong discharge curve after a cell swap. The fix is the same recalibration cycle: discharge the phone until it shuts off naturally, then charge uninterrupted to 100% with fast charging off. After one full cycle the gauge re-anchors and the shutdowns stop.