Cubot P9 Replacement Battery 3.7V 2000mAh Li-ion

Cubot P9 — 3.7V Li-ion Replacement Battery (P9)

This is a 3.7V, 2000mAh Li-ion cell for the Cubot P9 Android smartphone. It replaces the original internal battery when the existing cell has degraded, lost capacity, or no longer holds a charge. Voltage and capacity match the P9's power circuit requirements exactly.

• Cubot P9 fit: The P9 uses a direct internal cell mount with a fixed connector pinout tied to the phone's charge IC and fuel gauge IC. This cell matches that pinout and voltage rail — the BMS communicates correctly with the P9's power management hardware from first boot.
• Bench tested on actual hardware: We cycled this cell through charge and discharge under a simulated mixed-use load — screen, modem, and background tasks active. The BMS did not trip, and cell voltage held stable above the cutoff threshold through the full discharge curve.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle. This lets the fuel gauge IC map its coulomb counter to the new cell's actual discharge curve before high-current charging begins on an uncalibrated cell.

Why the Cubot P9 reports wrong battery percentage after a cell swap

The P9's fuel gauge IC stores a learned discharge curve from the original 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 but maps it against the old model, so percentages display incorrectly — often showing 100% that drops fast, or stalling at a fixed number. One full discharge to auto-off followed by an uninterrupted charge to 100% forces the IC to rewrite its calibration data against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the cell voltage drops below the phone's minimum threshold under a high-draw moment — modem handoff, screen brightness spike, or background sync — even though the fuel gauge still shows charge remaining. The P9's power management IC cuts power to protect the circuit, not because the cell is faulty. The fuel gauge is reading from an uncalibrated curve and overestimates remaining capacity at low voltages. Run the recalibration cycle first; if shutdowns persist below 3.2V under load, check that the connector is fully seated and the cell contacts are clean.