Infinix Note 2 BL-40BX Replacement Battery 3.8V 4000mAh

Infinix Note 2 X600 — 3.8V Li-Polymer Replacement Battery (BL-40BX)

The BL-40BX is a 3.8V, 4000mAh lithium-polymer cell that fits the Infinix Note 2 (X600). It replaces the original battery when capacity has dropped to the point where the phone can no longer hold a charge through a standard day. Dimensions are 88.36 × 63.38 × 4.80mm — verify these against your existing cell before fitting.

• Note 2 and X600 fitment: Both model names refer to the same hardware revision. They share the same battery bay dimensions, connector pinout, and BMS handshake protocol, so one cell covers both.
• Bench tested on actual hardware: We cycled the BL-40BX through full charge and load discharge on the Note 2 platform. The BMS accepted the cell without fault flags, and charge termination triggered correctly at 4.35V.
• Fuel gauge recalibration on first use: 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 fast charge current is applied to an uncalibrated cell.

Why the Note 2 reports wrong battery percentage after a cell swap

The Note 2 uses a coulomb counter that builds its percentage model against the old cell's impedance and discharge curve. A new cell has different internal resistance, so the counter starts reading inaccurately — often showing full charge dropping to 50% in minutes. The fix is one full uninterrupted discharge down to auto-shutoff, followed by a full charge to 100% with the screen off. After that cycle, the fuel gauge IC resets its reference points against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the modem or screen draws a current spike that drops cell voltage below the BMS cutoff threshold — even though the displayed percentage suggests charge remains. The new cell's voltage cliff is steeper than the aged cell the phone was calibrated to, so the BMS trips before the gauge catches up. Running the recalibration cycle described above tightens the gap between reported and actual voltage. If shutdowns continue after two full cycles, measure resting cell voltage — it should sit above 3.7V at 30% reported charge.