KTSP1950AA Karboon Wind W4 Compatible Battery 3.8V 1950mAh

Karboon Wind W4 — 3.8V Li-ion Replacement Battery (KTSP1950AA)

This is a 3.8V Li-ion cell rated at 1950mAh (7.41Wh), sized to fit the Karboon Wind W4 smartphone. It replaces the original KTSP1950AA unit when the factory cell no longer holds a charge or fails outright. Dimensions are 58.50 × 50.95 × 5.40mm — confirm these against your original before fitting.

• Wind W4 fitment: The Wind W4 uses a fixed connector pinout tied to the KTSP1950AA spec. This replacement matches that pinout, voltage rail, and physical footprint so the charge IC recognises the cell without a firmware flag.
• Bench tested on actual hardware: We cycled the cell through charge and discharge on a Wind W4 unit and confirmed the BMS accepted the cell, the charge IC hit the correct termination voltage, and no overcurrent faults were logged.
• Fuel gauge recalibration after fitting: On first use after installation, disable fast charging and run one full discharge-charge cycle at standard rate. This lets the fuel gauge IC map the new cell's discharge curve before the coulomb counter locks in its reference points — skipping this step is the main cause of erratic percentage readings.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC is still calibrated to the old degraded cell's voltage curve. The new cell's open-circuit voltage drops steeply under modem or screen load at the low end, hitting the hardware cutoff before the OS percentage reaches zero. The phone reads 25% but the cell voltage under load drops below 3.2V, triggering an emergency shutdown. One full unconstrained discharge-charge cycle recalibrates the coulomb counter and eliminates this in most cases.

Phone warm near the battery during the first few charges

A new Li-ion cell has slightly higher internal impedance than a broken-in cell, so the charge IC dissipates more heat during the constant-current phase. This is normal for the first two to three cycles and does not indicate a fault. Warmth should reduce noticeably by the third full charge. If the phone remains hot to the touch past cycle three, check that no third-party fast-charge adapter is overriding the Wind W4's charge rate.