Cubot S208A Replacement Battery 3.7V 1800mAh Li-ion

Cubot S208A / S208 — 3.7V Li-ion Replacement Battery (JLY15050100001)

This is a 3.7V, 1800mAh Li-ion cell for the Cubot S208A and S208 smartphones. It replaces OEM part JLY15050100001 when the original cell can no longer hold adequate charge for daily calls, messaging, and app use. Capacity is 1800mAh (6.66Wh) — identical to the factory specification.

• S208A and S208 compatibility: Both models use the same battery bay dimensions (70.65 × 59.80 × 4.10mm), the same 3.7V nominal rail, and the same connector pinout — one cell fits both variants without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the S208 platform. The BMS accepted the charge handshake on the first connection, and protection thresholds — overvoltage, undervoltage, and overcurrent — all triggered at expected values.
• First-cycle fuel gauge reset: On first use after installation, disable fast charging and run one full discharge-charge cycle. This lets the fuel gauge IC recalibrate its discharge curve against the new cell before high-current charging is applied to an uncalibrated register.

Why the S208 reports wrong battery percentage after a cell swap

The S208 uses a fuel gauge IC that tracks capacity by building a discharge model against the original cell over many cycles. Swap the cell and that learned curve no longer matches the new cell's chemistry. The gauge reads against old data, so it shows an incorrect state-of-charge — often optimistic in the upper range and pessimistic near the bottom. One full discharge to auto-off followed by a complete uninterrupted charge resets the coulomb counter and forces the IC to recalibrate against the new cell.

Sudden shutdown at 20–30% on the replacement cell

This happens because the fuel gauge IC still thinks the cell has usable capacity at 20–30%, but the actual cell voltage drops below the modem and display load threshold — typically around 3.4V under draw — and the BMS cuts the output to protect the cell. The old discharge curve predicted a gentler voltage drop; the new cell has a steeper cliff at a higher state-of-charge reading. Run two full discharge-charge cycles without interruption. After the second cycle the gauge recalibrates and the reported percentage aligns with real voltage — shutdowns stop occurring above 3.5V.