T-KING K1391 Replacement Battery 3.7V 2000mAh Li-ion

T-KING K1391 — 3.7V Li-ion Replacement Battery (K1391)

This is a 3.7V, 2000mAh Li-ion replacement battery for the T-KING K1391 smartphone. It fits directly into K1391 devices where the original cell has degraded and can no longer hold a working charge. Capacity is 2000mAh (7.4Wh) — matching the factory specification.

• K1391 platform fitment: The K1391 cell uses a specific connector pinout and physical footprint — 70.00 x 59.90 x 4.40mm — that matches the T-KING K1391 chassis. The BMS communicates over the same data line as the OEM cell, so the phone's charge IC accepts it without rejection flags.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench, monitoring BMS handshake behaviour and cutoff thresholds. The protection circuit triggers correctly at the low-voltage floor, and the charge IC accepted the cell without error on the second cycle after fuel gauge recalibration.
• First-cycle fast charge behaviour: After installation, disable fast charging for the first full discharge-charge cycle. The fuel gauge IC on the K1391 is calibrated to the old cell's discharge curve. Running a slow first cycle lets the coulomb counter reset against the new cell before fast charge current is applied to an uncalibrated gauge.

Why the K1391 reports wrong battery percentage after a cell swap

The K1391's fuel gauge IC builds its capacity model from repeated charge and discharge cycles on the original cell. When a new cell goes in, the stored discharge curve no longer matches the actual cell chemistry, so the percentage readout drifts — often showing full charge until a sudden drop. One complete slow charge and full discharge cycle forces the coulomb counter to relearn the new cell's voltage-to-capacity relationship. After that cycle, percentage tracking stabilises. Do not interrupt the first cycle early.

Sudden shutdown at 20–30% on the replacement cell

This happens when the modem, display, or both draw a current spike that drops the cell voltage below the BMS cutoff threshold — even though the gauge still shows charge remaining. On a new cell before calibration, the fuel gauge overestimates remaining capacity at low state-of-charge. The BMS then cuts output when voltage sags under load at what looks like 20–30%. Run two full discharge cycles without interruption to let the gauge IC map the actual low-voltage cliff of the new cell. After calibration, shutdown voltage should track closer to 3.2–3.3V under load.