ZTE Nubia Red Magic 6 Li3945T44P8H906455 Compatible Battery 3.85V 4850mAh

ZTE Nubia Red Magic 6 (NX669J) — 3.85V Li-Polymer Replacement Battery (Li3945T44P8H906455)

This is a 3.85V, 4850mAh Li-Polymer replacement battery for the ZTE Nubia Red Magic 6 (NX669J). It carries OEM part number Li3945T44P8H906455 and sits inside a gaming phone chassis built around sustained high-drain workloads. If the original cell has degraded and the phone is shutting down early or refusing to hold charge, this cell replaces it directly.

• Red Magic 6 / NX669J fit: Both model designations run the same 3.85V power rail, share the same battery connector, and require the same BMS handshake profile — so a single cell covers both variants without modification.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge passes on the NX669J. The BMS accepted the charge handshake on the first cycle, balanced correctly across the discharge curve, and hit the low-voltage cutoff at the expected threshold without tripping a premature shutdown.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. The fuel gauge IC on the Red Magic 6 was calibrated to the original cell's discharge curve — running one slow cycle gives the coulomb counter accurate reference points before high-current fast charging begins pushing current into an uncalibrated cell.

Sudden shutdown at 20–30% on the Red Magic 6 after a cell swap

The Red Magic 6 runs a Snapdragon 888 with a high-frequency display — both draw hard current spikes under gaming load. A new cell with an uncalibrated fuel gauge can report 25% remaining while the actual resting voltage has already dropped close to the BMS cutoff threshold. Under a sudden load spike — GPU ramp or modem burst — the cell voltage sags below 3.2V per cell for a split second, and the BMS cuts output to protect the cell. The phone reads this as a crash, not a low-battery event. Run two full slow discharge-charge cycles first; the coulomb counter will recalibrate and the reported percentage will track actual cell voltage accurately.

USB-PD fast charge not working on the first cycle after replacement

The Red Magic 6 uses a proprietary fast-charge protocol layered over USB-PD. After a cell swap, the charge IC sometimes falls back to standard 5V/2A on the first cycle because the BMS on the new cell has not yet completed its initial handshake with the phone's charge management IC. This is not a fault in the battery or the charger — it is the system defaulting to a safe rate until it has a confirmed cell profile. Complete one full charge cycle at the standard rate, then reconnect the original fast charger. The protocol negotiation should succeed from the second cycle onward.