Li3829T44P6h806435 Nubia Z11 Replacement Battery 3.85V 3000mAh

Nubia Z11 / NX531J — 3.85V Li-Polymer Replacement Battery (Li3829T44P6h806435)

This 3.85V, 3000mAh (11.55Wh) lithium-polymer cell is a direct swap for the battery in the Nubia Z11 and Z11 Dual SIM TD-LTE (NX531 / NX531J). It matches the OEM voltage rail and physical footprint — 79.50 × 63.10 × 3.40mm — so it seats correctly against the flex connector without modification. Swap it in when the original cell no longer holds a usable charge through a normal day.

• NX531 and NX531J compatibility: Both the standard Z11 and the Dual SIM TD-LTE variant run the same 3.85V power rail, use the same flex connector pinout, and pull from the same BMS handshake protocol — so a single cell covers the full Z11 line without revision differences.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on the NX531J. The BMS accepted the new cell without fault flags, charge current stepped correctly from pre-charge to CC/CV phase, and the protection circuit tripped at expected over-voltage and over-current thresholds.
• First-cycle fuel gauge reset: After installation, disable fast charging and complete one full discharge-to-charge cycle before resuming normal use. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging pushes amps into an uncalibrated cell.

Sudden shutdown at 20–30% on the Nubia Z11 after a cell swap

This is a voltage cliff, not a capacity problem. When the modem transmits or the screen peaks brightness, instantaneous current draw spikes hard — a new cell with an uncalibrated fuel gauge IC reads 25% state-of-charge but the open-circuit voltage has already sagged below the shutdown threshold. The phone cuts power to protect the SoC before the OS can log a low-battery event. One full discharge cycle from 100% to automatic shutdown, followed by an uninterrupted charge to 100%, gives the coulomb counter enough data to set an accurate low-voltage trip point. After that cycle, the 20–30% shutdowns stop.

Z11 not powering on after the replacement battery sat in storage

Li-polymer cells ship at around 50% state-of-charge, but if the phone or the battery sat unused for several months, the cell may have self-discharged below 2.5V — the BMS lockout threshold. At that voltage the protection circuit opens the output FET and the phone appears completely dead. Connect the original charger and leave it untouched for 20–30 minutes without pressing the power button; the charge IC trickle-charges at low current to recover the cell above the BMS re-enable threshold. Once voltage climbs above approximately 3.0V, the BMS closes the FET and normal charging resumes.