Cubot Note S Replacement Battery 3.7V 2500mAh Li-ion

Cubot Note S — 3.7V Li-ion Replacement Battery

This is a 3.7V, 2500mAh (9.25Wh) Li-ion replacement battery for the Cubot Note S smartphone. It replaces the original cell when capacity fade or outright failure makes the phone unreliable. Physical dimensions are 99.46 × 65.14 × 4.50mm — confirm these against your existing cell before fitting.

• Cubot Note S fitment: The Note S uses a fixed 3.7V nominal cell with no multi-voltage rail switching. This replacement matches that voltage, connector pin-out, and physical envelope so the battery seats correctly in the chassis pocket without modification.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the bench. The BMS held charge termination at the correct upper voltage threshold and did not trigger spurious cutoff under simulated modem and display load spikes.
• Fuel gauge recalibration after swap: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC re-map its coulomb counter against the new cell's actual discharge curve before high-current charging runs into an uncalibrated state.

Sudden shutdown at 20–30% on the replacement cell

The Cubot Note S fuel gauge IC retains the discharge curve from the old, degraded cell after a swap. When the new cell hits a voltage point the IC associates with near-empty on the old curve, it signals a low-voltage shutdown even though real capacity remains. The fix is one full uninterrupted discharge to automatic power-off followed by a full charge without interruption. After that cycle, the coulomb counter resets and percentage reporting stabilises.

Phone won't power on after the replacement cell sat in storage

Li-ion cells self-discharge in storage. If this battery dropped below approximately 2.5V per cell before installation, the BMS enters lockout mode to prevent charging a critically depleted cell. Plug into a known-good charger and leave it connected for 15–20 minutes without attempting to power on — the charge IC trickle-charges the cell back above the BMS recovery threshold. Once voltage recovers above 3.0V, the BMS releases lockout and normal charging resumes.