ZTE Nubia Z9 mini Li3829T44P6HA74140 Replacement Battery 3.8V 2900mAh

ZTE Nubia Z9 mini / NX511J — 3.8V Li-Polymer Replacement Battery (Li3829T44P6HA74140)

This is a 3.8V, 2900mAh Li-Polymer cell for the ZTE Nubia Z9 mini (NX511J) and Nubia Z9 (NX508). It replaces part number Li3829T44P6HA74140. The cell fits the original battery bay and connects to the same flex ribbon connector used across this handset family.

• NX511J and NX508 shared platform: Both the Nubia Z9 mini and Nubia Z9 run the same battery bay dimensions, connector pitch, and BMS handshake protocol — one cell covers both variants without modification.
• Bench tested on actual hardware: We ran this cell through full charge and discharge cycles on an NX511J test unit. The BMS accepted the cell without error flags, and the charge IC stepped through trickle, constant-current, and constant-voltage phases cleanly at rated current.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes energy into an uncalibrated coulomb counter — which is what causes erratic percentage readings early on.

Sudden shutdown at 20–30% on the Nubia Z9 mini after a cell swap

The Nubia Z9 mini's fuel gauge IC retains the discharge curve of the original — often degraded — cell. When a fresh 2900mAh cell is installed, the IC has no accurate curve to reference, so it misreports state-of-charge. Under modem or display load, the actual cell voltage drops faster than the gauge expects, and the phone hits the low-voltage cutoff while still displaying 20–30%. One complete slow discharge to auto-shutdown, followed by a full charge, resets the coulomb counter against the new cell's actual chemistry.

Device not powering on after the replacement cell sat in storage

Li-Polymer cells self-discharge during storage. If this cell has sat below 2.5V per cell, the BMS enters a protection lockout and blocks normal charging to prevent thermal runaway on an over-discharged cell. The phone will show nothing when plugged in. Connect to a wall charger — not a PC port — and leave it for 20–30 minutes before attempting to power on. Most BMS circuits on this platform will accept a trickle recovery charge and release the lockout once the cell returns to approximately 3.0V.