About this replacement
ZTE Nubia Play / Red Magic 5G Lite — 3.85V Li-Polymer Replacement Battery (LI3950T44P8H926251)
This is a 3.85V, 4900mAh (18.87Wh) Li-Polymer cell that replaces part number LI3950T44P8H926251. It fits the Nubia Play, Nubia Play 5G, Nubia Red Magic 5G Lite, and NX651J. Use it when the original cell has degraded and the phone can no longer hold a usable charge.
- NX651J platform fit: The Nubia Play, Nubia Play 5G, and Red Magic 5G Lite all share the same battery bay dimensions and connector pinout on the NX651J board revision. The BMS handshake protocol is identical across these variants, so one cell covers all three.
- Bench tested on actual hardware: We cycled this cell through full charge and discharge on the NX651J platform. The BMS accepted the cell without triggering a protection fault, and the charge IC negotiated its standard current profile without error flags.
- Fuel gauge recalibration on first cycle: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle at standard rate. This lets the fuel gauge IC map its coulomb counter against the new cell's discharge curve before high-current charging is applied to an uncalibrated cell.
Why the Nubia Play reports wrong battery percentage after a cell swap
The fuel gauge IC stores a learned discharge curve from the original cell. When you swap in a new cell, the IC still references the old curve, which causes the percentage readout to drift — often showing full charge when the cell is not actually full. The coulomb counter needs one uninterrupted full discharge and full charge cycle to reset its reference points. Until that cycle completes, percentage readings are unreliable. Let the phone drain to automatic shutdown, then charge to 100% without interruption.
Sudden shutdown at 20–30% on the replacement cell
This happens when the modem or display draws a current spike that drops the cell voltage below the BMS cutoff threshold — even though the gauge still reads 20–30%. A fresh cell with an uncalibrated fuel gauge is especially prone to this on the first few cycles. The BMS is working correctly; it cuts power when terminal voltage collapses under load, not when the percentage hits zero. Run the recalibration cycle described above, and check that the reported voltage stabilises above 3.6V under screen-on load before the percentage drops below 25%.