About this replacement
ZTE Grand S II — 3.8V Li-ion Replacement Battery (Li3830T43P4h835750)
This is a 3.8V, 3000mAh (11.4Wh) Li-ion cell built to replace the original battery in the ZTE Grand S II (S291). It fits the Grand S II and Grand S2 variants that use OEM part number Li3830T43P4h835750. Swap it in when the original cell no longer holds a charge through a normal day.
- Grand S II / S291 fit: The S291 and its Grand S2 variants share the same battery bay dimensions (83.40 × 56.65 × 5.02mm), voltage rail, and connector pinout. This cell slots in without modification and the BMS handshake clears on first boot.
- Bench tested on actual hardware: We cycled this cell on a Grand S II unit and monitored BMS communication through charge and load. The protection circuit tripped correctly at the low-voltage cutoff, and the charge IC accepted a full CC/CV cycle without fault codes.
- Fuel gauge recalibration on first use: On first installation, disable fast charging and run one complete discharge-to-charge cycle at standard current. This lets the fuel gauge IC map the new cell's discharge curve before the system pushes high current into an uncalibrated cell.
Sudden shutdown at 20–30% on the Grand S II after a cell swap
The Grand S II's fuel gauge IC stores a discharge curve calibrated to the original cell. A new cell with a different internal resistance profile causes the IC to misread state-of-charge. When the modem transmits or the screen peaks in brightness, the actual cell voltage drops below the protection threshold while the OS still shows 20–30% remaining. The BMS cuts power to protect the cell. Run one full uninterrupted discharge until the phone shuts off from depletion, then charge to 100% — this resets the coulomb counter against the new cell's actual curve.
Phone warm near the battery during the first few charge cycles
A fresh Li-ion cell has slightly higher internal impedance than a broken-in one. During the first two or three charge cycles, the charge IC works against that higher impedance, and the extra energy dissipates as heat in both the cell and the charge IC on the board. This is normal and tapers off as the cell conditions. If the phone stays warm past the third full cycle or feels hot rather than warm, check that the replacement cell's part number matches Li3830T43P4h835750 — a mismatched cell will sustain elevated impedance and abnormal heat.