Nubia V18 Li3940T44P6h876442 Replacement Battery 3.85V 4000mAh

Nubia V18 / NX612j — 3.85V Li-Polymer Replacement Battery (Li3940T44P6h876442)

This is a 3.85V, 4000mAh lithium-polymer cell that replaces the original battery in the Nubia V18 (NX612, NX612j) smartphone. It matches the OEM part number Li3940T44P6h876442 and fits the same physical bay at 85.85 × 63.00 × 4.30mm. Install it when the original cell no longer holds charge or causes unexpected shutdowns.

• NX612 / NX612j platform fit: Both model variants share the same battery bay dimensions, connector pinout, and BMS communication protocol — one cell covers all three listed model numbers without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the NX612 platform, confirmed the BMS handshake completed without fault codes, and verified the fuel gauge IC registered the full 4000mAh nominal capacity across multiple cycles.
• First-cycle fast-charge protocol: On first use after installation, turn off fast charging in the device settings and run one full discharge-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes current into an uncalibrated coulomb counter.

Why the Nubia V18 reports wrong battery percentage after a cell swap

The V18's fuel gauge IC builds its percentage readings from a stored discharge curve trained on the original cell. When a new cell goes in, that curve no longer matches the actual voltage-to-capacity relationship of the replacement. The IC will misread state-of-charge — often showing 100% too quickly or dropping percentage faster than the real capacity warrants. One full slow discharge down to automatic shutdown, followed by a full charge to 100%, forces the coulomb counter to rewrite its reference curve against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens when the modem radio or display draws a current spike that pulls cell voltage below the BMS cutoff threshold — even though the gauge still shows charge remaining. On a new cell that hasn't been calibrated, the IC can't accurately predict where that voltage cliff sits. The fix is the same full discharge-charge recalibration cycle. After one or two full cycles, the fuel gauge learns the cell's actual low-voltage floor and shuts down closer to true 0% rather than cutting at a false 25%.